Control system and method

ABSTRACT

Embodiments of the present invention provided a system comprising: a plurality of speed controllers each configured to assume one or more ‘on’ states or one or more ‘off’ states, in a predetermined one or more on states each speed controller being configured to cause a vehicle to operate in accordance with a target speed value, in an off state each speed controller being configured not to cause a vehicle to operate in accordance with a target speed value, the system being configured wherein only one of the speed controllers may be in an on state at a given moment in time, the other one or more speed controllers being arranged to assume an off state when a speed controller is in an on state, the system being configured to delete from a speed controller memory or associated speed controller memory directly accessible by said speed controller, one or more target speed values employed by a speed controller that is not in an on state.

INCORPORATION BY REFERENCE

The content of UK patent applications GB2492748, GB2492655 and GB2499252is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to vehicle speed control systems. Inparticular but not exclusively the invention relates to monitoring ofvehicle speed control systems to ensure correct operation.

BACKGROUND

In known vehicle speed control systems, typically referred to as cruisecontrol systems, the vehicle speed is maintained on-road once set by theuser without further intervention by the user so as to improve thedriving experience for the user by reducing workload.

With typical cruise control systems, the user selects a speed at whichthe vehicle is to be maintained, referred to as a set-speed, and thevehicle is maintained at a target speed that is set equal to theset-speed for as long as the user does not apply a brake or, in the caseof a vehicle having a manual transmission, depress a clutch pedal. Thecruise control system takes its speed signal from a driveshaft speedsensor or wheel speed sensors. When the brake or the clutch isdepressed, the cruise control system is disabled so that the user canoverride the cruise control system to change the vehicle speed withoutresistance from the system. If the user depresses the accelerator pedalby a sufficient amount the vehicle speed will increase, but once theuser removes his foot from the accelerator pedal the vehicle reverts tothe pre-set cruise speed (set-speed) by coasting.

Such systems are usually operable only above a certain speed, typicallyaround 15-20 kph, and are ideal in circumstances in which the vehicle istravelling in steady traffic conditions, and particularly on highways ormotorways. In congested traffic conditions, however, where vehicle speedtends to vary widely, cruise control systems are ineffective, andespecially where the systems are inoperable because of a minimum speedrequirement. A minimum speed requirement is often imposed on cruisecontrol systems so as to reduce the likelihood of low speed collision,for example when parking. Such systems are therefore ineffective incertain driving conditions (e.g. low speed) and are set to beautomatically disabled in circumstances in which a user may not considerit to be desirable to do so.

More sophisticated cruise control systems are integrated into the enginemanagement system and may include an adaptive functionality which takesinto account the distance to the vehicle in front using a radar-basedsystem. For example, the vehicle may be provided with a forward-lookingradar detection system so that the speed and distance of the vehicle infront is detected and a safe following speed and distance is maintainedautomatically without the need for user input. If the lead vehicle slowsdown, or another object is detected by the radar detection system, thesystem sends a signal to the engine or the braking system to slow thevehicle down accordingly, to maintain a safe following distance.

Known cruise control systems also cancel in the event that a wheel slipevent is detected requiring intervention by a traction control system(TC system or TCS) or stability control system (SCS). Accordingly, theyare not well suited to maintaining vehicle progress when driving in offroad conditions where such events may be relatively common.

It is an aim of embodiments of the present invention to addressdisadvantages associated with the prior art.

SUMMARY OF THE INVENTION

Embodiments of the invention may be understood with reference to theappended claims.

Aspects of the present invention provide an apparatus, a vehicle and amethod.

In one aspect of the invention for which protection is sought there isprovided a system comprising:

-   -   a plurality of speed controllers each configured to assume one        or more ‘on’ states or one or more ‘off’ states, in a        predetermined one or more on states each speed controller being        configured to cause a vehicle to operate in accordance with a        target speed value, in an off state each speed controller being        configured not to cause a vehicle to operate in accordance with        a target speed value,    -   the system being configured wherein only one of the speed        controllers may be in an on state at a given moment in time, the        other one or more speed controllers being arranged to assume an        off state when a speed controller is in an on state,    -   the system being configured not to retain in a memory accessible        by a speed controller a target speed value employed by a speed        controller that is not in an on state.

In one aspect of the invention for which protection is sought there isprovided a system comprising:

-   -   a plurality of speed controllers each configured to assume one        or more ‘on’ states or one or more ‘off’ states, in a        predetermined one or more on states each speed controller being        configured to cause a vehicle to operate in accordance with a        target speed value, in an off state each speed controller being        configured not to cause a vehicle to operate in accordance with        a target speed value,    -   the system being configured wherein only one of the speed        controllers may be in an on state at a given moment in time, the        other one or more speed controllers being arranged to assume an        off state when a speed controller is in an on state,    -   the system being configured to delete from a speed controller        memory or associated speed controller memory directly accessible        by said speed controller, one or more target speed values        employed by a speed controller that is not in an on state.

The system may be configured to delete from a speed controller memory orassociated speed controller memory directly accessible by said speedcontroller, any target speed values employed by a speed controller thatis not in an on state.

Some embodiments of the present invention have the advantage that,because when in an off state the speed controllers do not retain atarget speed value employed whilst in an on state in a memory accessibleto a speed controller, a risk that one speed controller utilises atarget speed value employed by another speed controller when that speedcontroller was in an on state is reduced. Thus the problem that a speedcontroller configured for controlling vehicle speed whilst travelling atrelatively low speeds, for example in off-road conditions or in urbanconditions, employs a relatively high target speed previously employedby an on-highway speed control system, such as a cruise control system,is reduced.

By retain is meant storage of data indicative of the target speed in amemory from which the data may be subsequently retrieved. In someembodiments by retain is meant storage of data indicative of the targetspeed in a memory from which the data may be retrieved by the system. Itis to be understood that in some embodiments target speed data may bestored in a data log associated with the vehicle, for example a centraldata log to allow vehicle usage and mode of usage to be monitored, thedata not being retrievable by any of the speed controllers.

It is to be understood that the system may be configured not to retainin a memory accessible by a speed controller a target speed valueemployed by a speed controller that is not in an on state by overwritingthe target speed value such that the target speed value is no longerstored. The system may for example overwrite the target speed value withdata that does not correspond to any target speed value, for examplewith a word such as a word ‘RESET’ instead of a numerical valuecorresponding to a target speed value. other arrangements are alsouseful.

It is to be understood that in principle a plurality of controllers maytransiently be in an on state substantially simultaneously, for examplein the course of one controller switching from an off state to an onstate and another controller switching from an on state to an off state.However it is to be understood that steady state operation of the systemwith more than one controller in an on state is prohibited.

It is to be understood that the controller or controllers describedherein may comprise a control unit or computational device having one ormore electronic processors. The system may comprise a single controlunit or electronic controller or alternatively different functions ofthe controller may be embodied in, or hosted in, different control unitsor controllers. As used herein the term “control unit” will beunderstood to include both a single control unit or controller and aplurality of control units or controllers collectively operating toprovide the stated control functionality. A set of instructions could beprovided which, when executed, cause said computational device toimplement the control techniques described herein. The set ofinstructions could be embedded in said one or more electronicprocessors. Alternatively, the set of instructions could be provided assoftware to be executed on said computational device. The speedcontroller may be implemented in software run on one or more processors.One or more other controllers may be implemented in software run on oneor more processors, optionally the same one or more processors as thespeed controller. Other arrangements are also useful.

Optionally, when a speed controller transitions from an on state to anoff state the system deletes from said memory one or more target speedvalues employed by that speed controller when in an on state.

Thus, one or more target speed values employed by a speed controllerwhen in an on state are not retained by the system when that speedcontroller is in an off state. Where a plurality of target speeds arestored, each may be deleted.

Optionally, in order to cause a vehicle to operate in accordance withthe target speed value, each speed controller is configured to generateat least one of:

-   -   a speed controller powertrain signal in order to cause a        powertrain to develop drive torque, and    -   a speed controller brake signal in order to cause application of        a brake to one or more wheels.

It is to be understood that in a predetermined one or more on states aspeed controller may generate the first controller powertrain signal soas to increase or decrease the amount of drive torque developed by apowertrain, and/or to generate the first controller brake signal, so asto cause the vehicle to operate in accordance with a target speed value.

Optionally each speed controller is configured to cause a vehicle tooperate in accordance with a target speed value by causing the vehicleto operate at a speed substantially equal to the target speed value.

In some embodiments a speed controller may cause the vehicle to travelat a speed substantially equal to the target speed value in the absenceof one or more conditions requiring a lower speed to be assumed. In someembodiments a speed controller may cause a reduction in vehicle speed inresponse to or in dependence on one or more terrain conditions, such asterrain surface roughness, surface coefficient of friction and/or one ormore other parameters.

In some embodiments one or more of the speed controllers may cause thepowertrain to develop negative drive torque by means of the powertrainsignal, for example by causing the powertrain to apply engine overrunbraking or by causing an electric propulsion machine coupled in or tothe powertrain to operate as a generator. A speed controller may causethe powertrain to develop negative drive torque, for example in responseto a reduction in an amount of powertrain torque demanded by the firstspeed controller so as to induce engine braking. In some embodiments thefirst speed controller may be configured to generate a powertrain signalcorresponding to a prescribed or required amount of negative powertraintorque as well as a prescribed or required amount of positive powertraintorque, as required. A speed controller associated with the powertrainmay be configured to control the powertrain to develop the prescribed orrequired amount of powertrain torque, whether positive or negative.

Optionally each of the plurality of speed controllers is configured toassume one of a plurality of ‘on’ states.

Optionally each of the speed controllers may assume a first or second onstate, in the second on state each speed controller being configured notto cause the vehicle to operate in accordance with the target speedvalue.

It is to be understood that the second on state may for examplecorrespond to a ‘standby’ on state in which the first controller doesnot cause application of brake torque or powertrain torque to controlvehicle speed in accordance with the target speed value.

It is to be understood that since only one speed controller may be in anon state at a given moment in time, only one speed controller may be inthe first or second on state at a given moment in time. If onecontroller is in the first or second on state the other one or morespeed controllers must assume or remain in an off state.

As described in more detail below, a speed controller may be operable toassume one of a plurality of off states including an off state and adisabled off state. A disabled off state may have the feature that oneor more additional conditions must be met before the speed controllermay assume an on state compared with an off state that is not a disabledoff state.

It is to be understood that in principle a plurality of controllers maytransiently be in an on state substantially simultaneously, for examplein the course of one controller switching from an off state to an onstate and another controller switching from an on state to an off state.However it is to be understood that steady state operation of the systemwith more than one controller in an on state is prohibited.

As noted above, the second on state may correspond to a standby state,for example a state in which the speed controller has a target speedstored therein and is primed to begin causing a vehicle to operate inaccordance with the target speed, but in which the speed controller doesnot cause the vehicle to operate in accordance with the target speedvalue. For example in the case that a driver overrides the speed controlsystem by depressing an accelerator pedal, causing a vehicle toaccelerate to a speed exceeding the target speed value, the speedcontroller may assume a standby on state until a driver releases theaccelerator pedal or until vehicle speed falls to or close to the targetspeed. Other arrangements may also be useful.

The speed controller may be configured automatically to resume operationin the first on state from the second on state when one or morepredetermined conditions are met, for example that the driver hasreleased the accelerator pedal following driver over ride, or vehiclespeed has fallen to a sufficiently close to or substantially equal tothe target speed value. Other arrangements are also useful.

Embodiments of the present invention may be useful in motorcycles, beingtwo wheeled motor vehicles, as well as in cars, trucks and other motorvehicles having two or more wheels.

Optionally the value of one or more target speeds stored in said memoryare deleted by overwriting the one or more stored target speed values.

As noted above the stored value may be overwritten with data that doesnot correspond to a speed. thus another speed controller seeking toaccess the stored value to use the stored value as a target speed valuewould be unable to use the stored value as a target speed value.

Optionally the system may be configured wherein when a speed controlleris in an off condition, a value of target speed previously employed bythat speed controller when in an on condition is retained in a memory ofthe system that is not accessible to the plurality of speed controllers.

Thus it is to be understood that in some embodiments the system may beconfigured to retain of value of target speed employed by a controllerthat is no longer in an on condition. The value of target speed may bestored in a memory from which none of the speed controllers can retrievethe target speed value, so as to prevent one speed controller fromemploying a value of target speed previously employed by another speedcontroller.

Optionally the system may be configured to retain the value of targetspeed used by a speed controller in a secure memory being a memory thatis not accessible to the plurality of speed controllers when the speedcontroller transitions to an off state.

Optionally the system may be operable to retrieve the value of targetspeed used by a speed controller from the secure memory when said speedcontroller is not in an off state.

Optionally the system may be operable to retrieve the value of targetspeed used by a speed controller from the secure memory when said speedcontroller subsequently assumes an on state.

Optionally the system may be configured wherein if the first speedcontroller is in an on state and a request is received to cause a secondspeed controller to assume an on state, the system is configured toallow the second speed controller to assume an on state at least in partin dependence on whether the first speed controller is causingapplication of a braking system.

Optionally the system may be configured wherein if the first speedcontroller is in an on state and a request is received to cause a secondspeed controller to assume an on state, the system is configured not toallow the second speed controller to assume an on state if the firstspeed controller is causing application of a braking system.

It is to be understood that the system may automatically cause thesecond speed controller to assume an on state, and therefore the firstcontroller to assume an off state, once the first controller terminatescausing application of a braking system. Alternatively the system maywait until a request is received to cause the second controller toassume an on state when the first controller is not causing applicationof a braking system before permitting the second speed controller toassume an on state.

Optionally the system may be configured wherein at least one of thespeed controllers is a controller of a cruise control system.

Optionally the system may be configured wherein at least one of thespeed controllers is a controller of an on-highway cruise control systemand at least one of the speed control systems is a controller of anoff-road cruise control system.

Other speed controllers may be employed in addition or instead such asqueue assist (QA) speed controllers, hill descent control (HDC) speedcontrollers or any other suitable speed controller.

In a further aspect of the invention for which protection is soughtthere is provided a vehicle comprising a system according to anotheraspect of the invention.

In one aspect of the invention for which protection is sought there isprovided a vehicle comprising a chassis, a body attached to saidchassis, a plurality of wheels, a powertrain to drive said wheels, abraking system to brake said wheels, and a system according to anotheraspect of the invention.

In one aspect of the invention for which protection is sought there isprovided a method of controlling a motor vehicle comprising:

-   -   causing each of a plurality of speed controllers to assume one        of or more ‘on’ states and one or more ‘off’ states,    -   when a controller is in a predetermined one or more on states        the method comprising causing a vehicle to operate in accordance        with a target speed value by means of said controller that is in        an on state,    -   when a controller is in an off state the method comprising not        causing a vehicle to operate in accordance with a target speed        value by means of said controller that is in an off state,    -   the method comprising allowing only one of the speed controllers        to be in an on state at a given moment in time and causing the        other one or more speed controllers to assume an off state when        a speed controller is in an on state,    -   the method further comprising not retaining in a memory        accessible by a speed controller a target speed value employed        by a speed controller that is not in an on state.

In an aspect of the invention for which protection is sought there isprovided a plurality of speed controllers each configured to assume oneof a plurality of respective states, in a first state each speedcontroller being configured to cause a vehicle to operate in accordancewith a target speed value, in a second state each speed controller beingconfigured not to cause a vehicle to operate in accordance with a targetspeed value, the system being configured wherein only one of the speedcontrollers may be in the first state at a given moment in time, theother one or more speed controllers being arranged to assume the secondstate when a speed controller is in the first state, wherein when in thesecond state the speed controllers do not retain a target speed valueemployed whilst the speed controller was in the first state.

In one aspect of the invention for which protection is sought there isprovided a method of controlling a motor vehicle comprising:

-   -   causing each of a plurality of speed controllers to assume one        of a plurality of respective states,    -   when a controller is in a first state the method comprising        causing a vehicle to operate in accordance with a target speed        value by means of a controller in the first state,    -   when a controller is in a second state the method comprising not        causing a vehicle to operate in accordance with a target speed        value by means of a controller in the second state,    -   the method comprising allowing only one of the speed controllers        to be in the first state at a given moment in time and causing        the other one or more speed controllers to assume the second        state when a speed controller is in the first state,    -   the method further comprising not retaining in a memory        accessible to a speed controller a target speed value employed        by a speed controller that is not in the first state.

In one aspect of the invention for which protection is sought there isprovided a system comprising:

-   -   a speed controller operable in plurality of states, in a        predetermined one or more ‘on’ states the controller being        configured to cause a vehicle to operate in accordance with a        target speed value, in an ‘off’ state the controller being        configured not to cause a vehicle to operate in accordance with        a target speed value; and    -   at least one torque invention controller configured        automatically to cause a change in an amount of torque applied        to at least one wheel in dependence on a value of one or more        torque intervention controller parameters,    -   wherein the system is configured to cause the speed controller        to assume a predetermined state in dependence on the value of        the one or more torque intervention parameters.

Optionally the system may be configured wherein the at least one torqueinvention controller is configured automatically to cause a change in anamount of torque applied to at least one wheel if a value of one or moretorque intervention controller parameters exceeds a first predeterminedthreshold value,

-   -   wherein if a value of one or more torque intervention controller        parameters exceeds a second predetermined threshold value        greater than the first the speed controller is configured to        assume the predetermined state.

The predetermined state may be a less functional state than the instantstate. That is, a state in which the speed controller is not permittedto perform as many functions as in the state from which it assumes thepredetermined state. Thus the predetermined state may be a state inwhich the controller may only cause application of brake torque by meansof a braking system, whilst the state from which the controller assumesthe predetermined state may be a state in which the controller may causeapplication of brake torque by means of a braking system and control anamount of powertrain drive torque delivered by a powertrain.

Alternatively the predetermined state may be an off state and the statefrom which the controller assumes the predetermined state may be a statein which the controller may cause application of brake torque by meansof a braking system and not an amount of powertrain drive torque bymeans of a powertrain.

Optionally the system may be configured wherein in at least a first onstate the speed controller is configured to cause a vehicle to operatein accordance with a target speed value by controlling an amount ofbrake torque delivered by means of a braking system and an amount ofpowertrain torque delivered by a powertrain.

It is to be understood that the speed controller may not necessarilycause application of (negative) brake torque and delivery of positivepowertrain drive torque substantially simultaneously. Furthermore thespeed controller may not necessarily cause application of brake torqueand delivery of positive powertrain drive torque substantiallycontinually, but only as required in order to cause a vehicle to operatein accordance with the target speed value.

Optionally the system may be configured wherein the speed controller isfurther operable in at least a second ‘on’ state in which the controlleris configured to cause a vehicle to operate in accordance with a targetspeed value by application of brake torque by means of a braking system,in the second ‘on’ state the controller being configured not to controlthe amount of powertrain drive torque delivered by means of apowertrain.

Optionally the system may be configured wherein when the speedcontroller is in the first ‘on’ state and the value of one or moretorque intervention controller parameters exceeds a second predeterminedthreshold greater than the first the speed controller is configuredautomatically to assume the second ‘on’ state.

Optionally the system may be configured wherein when the speedcontroller is in the second ‘on’ state and the value of one or moretorque intervention controller parameters exceeds a third predeterminedthreshold greater than the first the speed controller is configuredautomatically to assume an ‘off’ state.

Optionally the system may be configured wherein the third predeterminedthreshold value is greater than the second.

Optionally the system may be configured wherein the third predeterminedthreshold is less than the second.

Optionally the system may be configured wherein the third predeterminedthreshold is substantially equal to the second.

It is to be understood that the system may comprise a plurality oftorque intervention controllers. One or more of the torque interventioncontrollers may be configured automatically to cause a change in anamount of torque applied to at least one wheel in dependence on a valueof a different torque intervention controller parameter. For example atraction control system (TCS) may be configured automatically to cause areduction in an amount of positive torque applied to one or more wheelsin dependence on wheel slip, an anti-lock braking system (ABS) may beconfigured to cause a reduction in an amount of brake torque applied toone or more wheels also in dependence on wheel slip whilst a stabilitycontrol system (SCS) may be configured automatically to adjust an amountof torque applied to one or more wheels application in dependence on yawrate error being a difference or error between an expected value of yawrate for an instant steering angle and a measured value of yaw rate.Other torque intervention controllers such as a roll stability control(RSC) controller may be present in addition or instead.

In one aspect of the invention for which protection is sought there isprovided a vehicle comprising a system according to another aspect.

In one aspect of the invention for which protection is sought there isprovided a vehicle comprising a chassis, a body attached to saidchassis, a plurality of wheels, a powertrain to drive said wheels, abraking system to brake said wheels, and a system according to anotheraspect.

In one aspect of the invention for which protection is sought there isprovided a method of controlling a vehicle comprising:

-   -   causing a speed controller to assume an ‘on’ states or an ‘off’        state,    -   when the speed controller is in a predetermined one or more on        states the method comprising causing the vehicle to operate in        accordance with a target speed value by means of the speed        controller,    -   when the speed controller is in an ‘off’ state the method        comprising not causing the vehicle to operate in accordance with        a target speed value,    -   the method comprising automatically causing a change in an        amount of torque applied to at least one wheel by means of at        least one torque invention controller in dependence on a value        of one or more torque intervention controller parameters,    -   the method comprising causing the speed controller to assume a        predetermined state in dependence on the value of the one or        more torque intervention parameters.

The method may comprise automatically causing a change in an amount oftorque applied to at least one wheel by means of at least one torqueinvention controller if a value of one or more torque interventioncontroller parameters exceeds a first predetermined threshold value.

The method may comprise causing the speed controller to assume thepredetermined state if a value of one or more torque interventioncontroller parameters exceeds a second predetermined threshold valuegreater than the first.

In one aspect of the invention for which protection is sought there isprovided a carrier medium carrying computer readable code forcontrolling a vehicle to carry out the method of another aspect.

In one aspect of the invention for which protection is sought there isprovided a computer program product executable on a processor so as toimplement the method of another aspect.

In one aspect of the invention for which protection is sought there isprovided a computer readable medium loaded with the computer programproduct of another aspect.

In one aspect of the invention for which protection is sought there isprovided a processor arranged to implement the method of another aspect,or the computer program product of another aspect.

In an aspect of the invention for which protection is sought there isprovided a system comprising: a plurality of speed controllers eachconfigured to assume one of a plurality of respective states, in a firststate each speed controller being configured to cause a vehicle tooperate in accordance with a target speed value, in a second state eachspeed controller being configured not to cause a vehicle to operate inaccordance with a target speed value, the system being configuredwherein only one of the speed controllers may be in the first state at agiven moment in time, the other one or more speed controllers beingarranged to assume the second state when a speed controller is in thefirst state, the system being configured not to retain in a memoryaccessible to a speed controller a target speed value employed by aspeed controller that is not in the first state.

It is to be understood that in principle a plurality of controllers maytransiently be in the first states substantially simultaneously, forexample in the course of one controller switching from the second stateto the first state and another controller switching from the first stateto the second state. However it is to be understood that steady stateoperation of the system with more than one controller in the first stateis prohibited.

Within the scope of this application it is envisaged that the variousaspects, embodiments, examples and alternatives, and in particular theindividual features thereof, set out in the preceding paragraphs, in theclaims and/or in the following description and drawings, may be takenindependently or in any combination. For example features described inconnection with one embodiment are applicable to all embodiments, unlesssuch features are incompatible.

For the avoidance of doubt, it is to be understood that featuresdescribed with respect to one aspect of the invention may be includedwithin any other aspect of the invention, alone or in appropriatecombination with one or more other features.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by wayof example only, with reference to the accompanying figures in which:

FIG. 1 is a schematic illustration of a vehicle according to anembodiment of the invention in plan view;

FIG. 2 shows the vehicle of FIG. 1 in side view;

FIG. 3 is a high level schematic diagram of an embodiment of the vehiclespeed control system of the present invention, including a cruisecontrol system and a low-speed progress control system;

FIG. 4 is a schematic diagram of further features of the vehicle speedcontrol system in FIG. 3;

FIG. 5 illustrates a steering wheel and brake and accelerator pedals ofa vehicle according to an embodiment of the present invention;

FIG. 6 is a schematic illustration of a known key fob for use with thevehicle of FIG. 1;

FIG. 7 is a flowchart illustrating a method of operation of a vehicleaccording to an embodiment of the present invention;

FIG. 8 is a flowchart illustrating a method of operation of a vehicleaccording to an embodiment of the present invention;

FIG. 9 is a flowchart illustrating a method of operation of a vehicleaccording to an embodiment of the present invention; and

FIG. 10 is a flowchart illustrating a method of operation of a vehicleaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

References herein to a block such as a function block are to beunderstood to include reference to software code for performing thefunction or action specified which may be an output that is providedresponsive to one or more inputs. The code may be in the form of asoftware routine or function called by a main computer program, or maybe code forming part of a flow of code not being a separate routine orfunction. Reference to function block is made for ease of explanation ofthe manner of operation of embodiments of the present invention.

FIG. 1 shows a vehicle 100 according to an embodiment of the presentinvention. The vehicle 100 has a powertrain 129 that includes an engine121 that is connected to a driveline 130 having an automatictransmission 124. It is to be understood that embodiments of the presentinvention are also suitable for use in vehicles with manualtransmissions, continuously variable transmissions or any other suitabletransmission.

In the embodiment of FIG. 1 the transmission 124 may be set to one of aplurality of transmission operating modes, being a park mode P, areverse mode R, a neutral mode N, a drive mode D or a sport mode S, bymeans of a transmission mode selector dial 124S. The selector dial 124Sprovides an output signal to a powertrain controller 11 in response towhich the powertrain controller 11 causes the transmission 124 tooperate in accordance with the selected transmission mode.

The driveline 130 is arranged to drive a pair of front vehicle wheels111,112 by means of a front differential 137 and a pair of front driveshafts 118. The driveline 130 also comprises an auxiliary drivelineportion 131 arranged to drive a pair of rear wheels 114, 115 by means ofan auxiliary driveshaft or prop-shaft 132, a rear differential 135 and apair of rear driveshafts 139. The front wheels 111, 112 in combinationwith the front drive shafts 118 and front differential 137 may bereferred to as a front axle 136F. The rear wheels 114, 115 incombination with rear drive shafts 139 and rear differential 135 may bereferred to as a rear axle 136R.

The wheels 111, 112, 114, 115 each have a respective brake 111B, 112B,114B, 115B. Respective speed sensors 111S, 112S, 114S, 115S areassociated with each wheel 111, 112, 114, 115 of the vehicle 100. Thesensors 111S, 112S, 114S, 115S are mounted to a chassis 100C of thevehicle 100 and arranged to measure a speed of the corresponding wheel.

Embodiments of the invention are suitable for use with vehicles in whichthe transmission is arranged to drive only a pair of front wheels oronly a pair of rear wheels (i.e. front wheel drive vehicles or rearwheel drive vehicles) or selectable two wheel drive/four wheel drivevehicles. In the embodiment of FIG. 1 the transmission 124 is releasablyconnectable to the auxiliary driveline portion 131 by means of a powertransfer unit (PTU) 131P, allowing operation in a two wheel drive modeor a four wheel drive mode. It is to be understood that embodiments ofthe invention may be suitable for vehicles having more than four wheelsor where only two wheels are driven, for example two wheels of a threewheeled vehicle or four wheeled vehicle or a vehicle with more than fourwheels.

A control system for the vehicle engine 121 includes a centralcontroller 10, referred to as a vehicle control unit (VCU) 10, thepowertrain controller 11, a brake controller 13 and a steeringcontroller 170C. The brake controller 13 is an anti-lock braking system(ABS) controller 13 and forms part of a braking system 22 (FIG. 3). TheVCU 10 receives and outputs a plurality of signals to and from varioussensors and subsystems (not shown) provided on the vehicle. The VCU 10includes a low-speed progress (LSP) control system 12 shown in FIG. 3, astability control system (SCS) 14S, a traction control system (TCS) 14T,a cruise control system 16 and a Hill Descent Control (HDC) system 12HD.The SCS 14S improves stability of the vehicle 100 by detecting andmanaging loss of traction when cornering. When a reduction in steeringcontrol is detected, the SCS 14S is configured automatically to commanda brake controller 13 to apply one or more brakes 111B, 112B, 114B, 115Bof the vehicle 100 to help to steer the vehicle 100 in the direction theuser wishes to travel. If excessive wheel spin is detected, the TCS 14Sis configured to reduce wheel spin by application of brake force incombination with a reduction in powertrain drive torque. In theembodiment shown the SCS 14S and TCS 14T are implemented by the VCU 10.In some alternative embodiments the SCS 14S and/or TCS 14T may beimplemented by the brake controller 13. Further alternatively, the SCS14S and/or TCS 14T may be implemented by separate controllers.

Similarly, one or more of the controllers 10, 11, 13, 170C may beimplemented in software run on a respective one or more computingdevices such as one or more electronic control units (ECUs). In someembodiments two or more controllers may be implemented in software runon one or more common computing devices. Two or more controllers may beimplemented in software in the form of a combined software module, or aplurality of respective modules each implementing only one controller.

One or more computing devices may be configured to permit a plurality ofsoftware modules to be run on the same computing device withoutinterference between the modules. For example the computing devices maybe configured to allow the modules to run such that if execution ofsoftware code embodying one module terminates erroneously, or thecomputing device enters an unintended endless loop in respect of one ofthe modules, it does not affect execution by one or more computingdevices of software code comprised by a software module embodying thesecond controller.

It is to be understood that one or more of the controllers 10, 11, 13,170C may be configured to have substantially no single point failuremodes, i.e. one or more of the controllers may have dual or multipleredundancy. It is to be understood that robust partitioning technologiesare known for enabling redundancy to be introduced, such as technologiesenabling isolation of software modules being executed on a commoncomputing device. It is to be understood that the common computingdevice will typically comprise at least one microprocessor, optionally aplurality of processors, which may operate in parallel with one another.In some embodiments a monitor may be provided, the monitor beingoptionally implemented in software code and configured to raise an alertin the event a software module is determined to have malfunctioned.

The SCS 14S, TCS 14T, ABS controller 22C and HDC system 12HD provideoutputs indicative of, for example, SCS activity, TCS activity and ABSactivity including brake interventions on individual wheels and enginetorque requests from the VCU 10 to the engine 121, for example in theevent a wheel slip event occurs. Each of the aforementioned eventsindicate that a wheel slip event has occurred. Other vehicle sub-systemssuch as a roll stability control system or the like may also be present.

As noted above the vehicle 100 includes a cruise control system 16 whichis operable to automatically maintain vehicle speed at a selected speedwhen the vehicle is travelling at speeds in excess of 25 kph. The cruisecontrol system 16 is provided with a cruise control HMI (human machineinterface) 18 by which means the user can input a target vehicle speedto the cruise control system 16 in a known manner. In one embodiment ofthe invention, cruise control system input controls are mounted to asteering wheel 171 (FIG. 5). The cruise control system 16 may beswitched on by pressing a cruise control system selector button 176.When the cruise control system 16 is switched on, depression of a‘set-speed’ control 173 sets the current value of a cruise controlset-speed parameter, cruise_set-speed to the current vehicle speed.Depression of a ‘+’ button 174 allows the value of cruise_set-speed tobe increased whilst depression of a ‘−’ button 175 allows the value ofcruise_set-speed to be decreased. A resume button 173R is provided thatis operable to control the cruise control system 16 to resume speedcontrol at the instant value of cruise_set-speed following driverover-ride. It is to be understood that known on-highway cruise controlsystems including the present system 16 are configured so that, in theevent that the user depresses the brake or, in the case of vehicles witha manual transmission, a clutch pedal, the cruise control function iscancelled and the vehicle 100 reverts to a manual mode of operationwhich requires accelerator pedal input by a user in order to maintainvehicle speed. In addition, detection of a wheel slip event, as may beinitiated by a loss of traction, also has the effect of cancelling thecruise control function. Speed control by the system 16 is resumed ifthe driver subsequently depresses the resume button 173R.

The cruise control system 16 monitors vehicle speed and any deviationfrom the target vehicle speed is adjusted automatically so that thevehicle speed is maintained at a substantially constant value, typicallyin excess of 25 kph. In other words, the cruise control system isineffective at speeds lower than 25 kph. The cruise control HMI 18 mayalso be configured to provide an alert to the user about the status ofthe cruise control system 16 via a visual display of the HMI 18. In thepresent embodiment the cruise control system 16 is configured to allowthe value of cruise_set-speed to be set to any value in the range 25-150kph.

The LSP control system 12 also provides a speed-based control system forthe user which enables the user to select a very low target speed atwhich the vehicle can progress without any pedal inputs being requiredby the user. Low-speed speed control (or progress control) functionalityis not provided by the on-highway cruise control system 16 whichoperates only at speeds above 25 kph.

The LSP control system 12 is activated by means of a LSP control systemselector button 172 mounted on the steering wheel 171. The system 12 isoperable to apply selective powertrain, traction control and brakingactions to one or more wheels of the vehicle 100, collectively orindividually, to maintain the vehicle 100 at the desired speed.

The LSP control system 12 is configured to allow a user to input adesired value of set-speed parameter, LSP_set-speed to the LSP controlsystem 12 via a low-speed progress control HMI (LSP HMI) 20 (FIG. 1,FIG. 3) which shares certain input buttons 173-175 with the cruisecontrol system 16 and HDC control system 12HD. Provided the vehiclespeed is within the allowable range of operation of the LSP controlsystem (which is the range from 2 to 30 kph in the present embodimentalthough other ranges are also useful) the LSP control system 12controls vehicle speed in accordance with the value of LSP_set-speed.Unlike the cruise control system 16, the LSP control system 12 isconfigured to operate independently of the occurrence of a tractionevent. That is, the LSP control system 12 does not cancel speed controlupon detection of wheel slip. Rather, the LSP control system 12 activelymanages vehicle behaviour when slip is detected.

The LSP control HMI 20 is provided in the vehicle cabin so as to bereadily accessible to the user. The user of the vehicle 100 is able toinput to the LSP control system 12, via the LSP HMI 20, an indication ofthe speed at which the user desires the vehicle to travel (referred toas “the target speed”) by means of the ‘set-speed’ button 173 and the‘+’/‘−’ buttons 174, 175 in a similar manner to the cruise controlsystem 16. The LSP HMI 20 also includes a visual display upon whichinformation and guidance can be provided to the user about the status ofthe LSP control system 12.

The LSP control system 12 receives an input from the braking system 22of the vehicle indicative of the extent to which the user has appliedbraking by means of the brake pedal 163. The LSP control system 12 alsoreceives an input from an accelerator pedal 161 indicative of the extentto which the user has depressed the accelerator pedal 161. An input isalso provided to the LSP control system 12 from the transmission orgearbox 124. This input may include signals representative of, forexample, the speed of an output shaft of the gearbox 124, torqueconverter slip and a gear ratio request. Other inputs to the LSP controlsystem 12 include an input from the cruise control HMI 18 which isrepresentative of the status (ON/OFF) of the cruise control system 16,and an input from the LSP control HMI 20.

The HDC system 12HD is configured to limit vehicle speed when descendinga gradient. When the HDC system 12HD is active, the system 12HD controlsthe braking system 22 (via brake controller 13) in order to limitvehicle speed to a value corresponding to that of a HDC set-speedparameter HDC_set-speed which may be set by a user. The HDC set-speedmay also be referred to as an HDC target speed. Provided the user doesnot override the HDC system by depressing the accelerator pedal when theHDC system 12HD is active, the HDC system 12HD controls the brakingsystem 22 to prevent vehicle speed from exceeding the value ofHDC_set-speed. In the present embodiment the HDC system 12HD is notoperable to apply positive drive torque. Rather, the HDC system 12HD isonly operable to apply negative brake torque by means of the brakingsystem 22.

A HDC system HMI 20HD is provided by means of which a user may controlthe HDC system 12HD, including setting the value of HDC_set-speed. AnHDC system selector button 177 is provided on the steering wheel 171 bymeans of which a user may activate the HDC system 12HD to controlvehicle speed.

As noted above, the HDC system 12HD is operable to allow a user to set avalue of HDC set-speed parameter HDC_set-speed and to adjust the valueof HDC_set-speed using the same controls as the cruise control system 16and LSP control system 12. Thus, in the present embodiment, when the HDCsystem 12HD is controlling vehicle speed, the HDC system set-speed maybe increased, decreased or set to an instant speed of the vehicle in asimilar manner to the set-speed of the cruise control system 16 and LSPcontrol system 12, using the same control buttons 173, 173R, 174, 175.The HDC system 12HD is operable to allow the value of HDC_set-speed tobe set to any value in the range from 2-30 kph.

If the HDC system 12HD is selected when the vehicle 100 is travelling ata speed of 50 kph or less and no other speed control system is inoperation, the HDC system 12HD sets the value of HDC_set-speed to avalue selected from a look-up table. The value output by the look-uptable is determined in dependence on the identity of the currentlyselected transmission gear, the currently selected PTU gear ratio(Hi/LO) and the currently selected driving mode. The HDC system 12HDthen applies the powertrain 129 and/or braking system 22 to slow thevehicle 100 to the HDC system set-speed provided the driver does notoverride the HDC system 12HD by depressing the accelerator pedal 161.The HDC system 12HD is configured to slow the vehicle 100 to theset-speed value at a deceleration rate not exceeding a maximum allowablerate although as noted elsewhere the HDC system 12HD is not able tocause positive drive torque to be applied by the powertrain 129 in orderto reduce a rate of deceleration of the vehicle 100. The rate is set at1.25 ms-2 in the present embodiment, however other values are alsouseful. If the user subsequently presses the ‘set-speed’ button 173 theHDC system 12HD sets the value of HDC_set-speed to the instant vehiclespeed provided the instant speed is 30 kph or less. If the HDC system12HD is selected when the vehicle 100 is travelling at a speed exceeding50 kph, the HDC system 12HD ignores the request and provides anindication to the user that the request has been ignored.

In the present embodiment the vehicle 100 is configured to assume one ofa plurality of power modes PM at a given moment in time. In each powermode the vehicle 100 may be operable to allow a predetermined set of oneor more operations to be performed. For example, the vehicle 100 mayallow a predetermined one or more vehicle subsystems such as aninfotainment system, a windscreen demist subsystem and a windscreenwiper control system to be activated only in a respective one or morepredetermined power modes. In one or more of the power modes the vehicle100 may be configured to inhibit one or more operations, such as turningon of the infotainment system.

The identity of the power mode in which the vehicle 100 is to operate ata given moment in time is transmitted to each controller 10, 11, 12, 13,14, 16, 12HD, of the vehicle 100 by the central controller 10. Thecontrollers respond by assuming a predetermined state associated withthat power mode and that controller. In the present embodiment eachcontroller may assume an ON state in which the controller is configuredto execute computer program code associated with that controller, and anOFF state in which supply of power to the controller is terminated. Inthe present embodiment, the central controller 10 is also operable toassume a quiescent state. The quiescent state is assumed by the centralcontroller 10 when the vehicle is in power mode PM0 and the controller10 has confirmed that the other controllers 11, 12, 13, 14, 16, 12HDhave successfully assumed the OFF state following receipt of the commandto assume power mode PM0.

In the present embodiment the vehicle 100 is provided with a known keyfob 190 (FIG. 6) that has a radio frequency identification device (RFID)190R embedded therein. The key fob 190 has first and second controlbuttons 191, 192. The key fob 100 is configured to generate a respectiveelectromagnetic signal in response to depression of the first or secondcontrol buttons 191, 192. The central controller 10 detects theelectromagnetic signal by means of a receiver module forming part of thecontroller 10 and triggers locking or unlocking of door locks 182L ofthe vehicle 100. Each door 100D of the vehicle 100 is provided with arespective door lock 182L as shown in FIG. 2.

Pressing of the first control button 191 generates a door unlock signal,which triggers unlocking of the door locks 182L, whilst pressing of thesecond control button 192 triggers a door lock signal, which triggerslocking of the door locks 182L.

When the controller 10 is in the quiescent state, consumption of powerby the central controller 10 is reduced and the controller 10 monitorsreceipt of a door unlock signal from the key fob 190. It is to beunderstood that in some embodiments one or more vehicle controllers maybe configured to remain in the ON or quiescent state, to allow one ormore essential functions to be performed, when the vehicle is in powermode PM0. For example in vehicles fitted with an intruder alarm systeman intruder alarm controller may be permitted to remain in the ON or aquiescent state pending detection of an intrusion. Upon detection of anintrusion the intruder alarm controller may cause the central controller10 to assume the ON state if it is not already in that state.

The central controller 10 is also configured to transmit a radiofrequency (RF) ‘interrogation’ signal that causes the RFID device 190Rof the key fob 190 to generate an RF ‘acknowledgement’ signal inresponse to receipt of the interrogation signal. In the presentembodiment the RFID device 190R is a passive device, not requiringbattery power in order to generate the acknowledgement signal. Thecontroller 10 is configured to detect the acknowledgment signaltransmitted by the RFID device 190R provided the RFID device 190R iswithin range. By the term ‘within range’ is meant that the RFID device190R or fob 190 is sufficiently close to the controller 10 to receivethe interrogation signal and generate an acknowledgement signal that isdetectable by the controller 10.

The vehicle 100 is also provided with a start/stop button 181. Thestart/stop button 181 is configured to transmit a signal to the centralcontroller 10 when pressed in order to trigger an engine startoperation, provided certain predetermined conditions are met. Inresponse to pressing of the start/stop button 181 the central controller10 causes the vehicle 100 to be placed in a condition in which if thetransmission 124 is subsequently placed in the forward driving mode D orreverse driving mode R, the vehicle 100 may be driven by depressingaccelerator pedal 161. In the present embodiment, the central controller10 is configured to perform a pre-start verification operation beforecommanding the powertrain controller 11 to trigger an engine startoperation. In performing the pre-start verification operation thecontroller 10 verifies (a) that the vehicle 100 is in a predeterminedpower mode as described in more detail below, (b) that the controller 10is receiving an acknowledgement signal from the key fob 190 in responseto transmission of the interrogation signal by the controller 10, and(c) that the transmission 124 is in either the park P or neutral Nmodes. Thus, the controller 10 requires that the RFID device 190R iswithin range of the controller 10 before permitting an engine start. Ifany of conditions (a) to (c) are not met the controller causes thevehicle 100 to remain in its current power mode.

It is to be understood that the central controller 10 is configured tocause the vehicle 100 to assume a predetermined one of a plurality ofpower modes in dependence at least in part on actuation of a controlbutton 191, 192 of the key fob 190 and actuation of the start/stopbutton 181. In some embodiments the vehicle 100 may be configured suchthat the central controller 10 responds to voice commands from a user inaddition to or instead of signals received from the key fob 190.

The various power modes in which the vehicle 100 of the embodiment ofFIG. 1 may be operated will now be described. As noted above, the keyfob 190 is operable to cause the door locks 182L of the vehicle 100 tobe locked and unlocked. When the doors 100D of the vehicle 100 (FIG. 2)are closed and the locks 182L are in the locked condition, the vehicle100 assumes power mode PM0.

If the first button 191 of the key fob 190 is subsequently actuated, thecontroller 10 causes the door locks 182L to assume the unlockedcondition. Once the door locks 182L are in the unlocked condition andthe controller 10 detects the acknowledgement signal from the key fob190, the controller 10 causes the vehicle 100 to assume power mode PM4.In power mode PM4 the controller 10 permits a predetermined number ofelectrical systems to become active, including an infotainment system.Power mode PM4 may also be referred to as a convenience mode oraccessory mode. If a user subsequently presses the second button 192 ofthe key fob 190, the controller 10 causes the vehicle 100 to revert topower mode PM0.

If, whilst the vehicle is in power mode PM4 a user presses the starterbutton 181 and maintains the button 181 in a depressed condition, thecontroller 10 performs the pre-start verification operation describedabove. Provided conditions (a) to (c) of the pre-start verificationoperation are met, the controller 10 places the vehicle 100 in powermode PM6. When the vehicle 100 is in power mode PM6 the powertraincontroller 11 is permitted to activate a starter device. In the presentembodiment the starter device is a starter motor 121M. The powertraincontroller 11 is then commanded to perform an engine start operation inwhich the engine 121 is cranked by means of the starter motor 121M tocause the engine 121 to start. Once the controller 10 determines thatthe engine 121 is running, the controller 10 places the vehicle 100 inpower mode PM7.

In power mode PM6 the controller 10 disables certain non-criticalelectrical systems including the infotainment system. This is at leastin part so as to reduce the magnitude of the electrical load on abattery 100B of the vehicle during cranking in order to permit anincrease in the amount of electrical current available for enginestarting. Isolation of non-critical electrical systems also reduces arisk of damage to the systems when a relatively large current drain isplaced on the battery 100B by the starter motor 121M.

If whilst the vehicle is in power mode PM7, with the engine 121 running,a user again actuates the start/stop button 181, the controller 10causes the powertrain controller 11 to switch off the engine 121 and thecontroller 10 causes the vehicle 100 to transition to power mode PM4. Auser may then cause the vehicle to assume power mode PM0 by pressing thefirst button 191 of the key fob 190 provided each of the doors 100D isclosed. It is to be understood that in some embodiments the user maytrigger assumption of power mode PM0 whilst remaining in the vehicle 100and locking the doors 181 by means of the key fob 190. In someembodiments the vehicle 100 may be configured to assume power mode PM0regardless of whether the controller is receiving the acknowledgementsignal from the key fob 190. Other arrangements are also useful.

It is to be understood that assumption of power mode PM0 by the vehicle100 may be referred to as ‘key off’, whilst assumption of power mode PM4from power mode PM0 may be referred to as ‘key on’. A sequence oftransitions of the vehicle from power mode PM0 to PM4, and back to powermode PM0, optionally including one or more transitions to power mode PM6and power mode PM7 prior to assumption of power mode PM0, may bereferred to as a ‘key cycle’. Thus a key cycle begins and ends with thevehicle 100 in power mode PM0. In some embodiments, assumption of powermode PM6 or PM7 from power mode PM0 may be required in order to completea key cycle, starting with power mode PM0.

It is to be understood that the VCU 10 is configured to implement aknown Terrain Response (TR)™ System of the kind described above in whichthe VCU 10 controls settings of one or more vehicle systems orsub-systems such as the powertrain controller 11 in dependence on aselected driving mode. The driving mode may be selected by a user bymeans of a driving mode selector 141S (FIG. 1). The driving modes mayalso be referred to as terrain modes, terrain response modes, or controlmodes. In the embodiment of FIG. 1 four driving modes are provided: an‘on-highway’ driving mode suitable for driving on a relatively hard,smooth driving surface where a relatively high surface coefficient offriction exists between the driving surface and wheels of the vehicle; a‘sand’ driving mode suitable for driving over sandy terrain; a ‘grass,gravel or snow’ driving mode suitable for driving over grass, gravel orsnow, a ‘rock crawl’ driving mode suitable for driving slowly over arocky surface; and a ‘mud and ruts’ driving mode suitable for driving inmuddy, rutted terrain. Other driving modes may be provided in additionor instead.

In the present embodiment, at any given moment in time the LSP controlsystem 12 is in one of a plurality of allowable ‘on’ modes (alsoreferred to as conditions or states) selected from amongst an active orfull function (FF) mode, a descent control (DC) mode, also referred toas an intermediate mode and a standby mode. The LSP control system mayalso assume an ‘off’ mode or condition. The active mode, DC mode andstandby mode may be considered to be different ‘on’ modes or conditionsof the vehicle, i.e. different modes in which the LSP control system isin an ‘on’ mode or condition as opposed to an ‘off’ mode or condition.In the off condition the LSP control system 12 only responds to pressingof the LSP selector button 172, which causes the LSP control system 12to assume the on condition and the DC mode.

In the active or full function mode, the LSP control system 12 activelymanages vehicle speed in accordance with the value of LSP set-speed,LSP_set-speed, by causing the application of positive powertrain drivetorque to one or more driving wheels or negative braking system torqueto one or more braked wheels.

In the DC mode the LSP control system 12 operates in a similar manner tothat in which it operates when in the active mode except that the LSPcontrol system 12 is prevented from commanding the application ofpositive drive torque by means of the powertrain 129. Rather, onlybraking torque may be applied, by means of the braking system 22 and/orpowertrain 129. The LSP control system 12 is configured to increase ordecrease the amount of brake torque applied to one or more wheels inorder to cause the vehicle to maintain the LSP set-speed to the extentpossible without application of positive drive torque. It is to beunderstood that, in the present embodiment, operation of the LSP controlsystem 12 in the DC mode is very similar to operation of the HDC system12HD, except that the LSP control system 12 continues to employ the LSPcontrol system 12 set-speed value LSP_set-speed rather than the HDCcontrol system set-speed value HDC_set-speed.

In the standby mode, the LSP control system 12 is unable to causeapplication of positive drive torque or negative brake torque to awheel.

As noted above, in the ‘off’ mode the LSP control system 12 is notresponsive to any LSP input controls except the LSP control systemselector button 172. Pressing of the LSP control system selector button172 when the system 12 is in the off mode causes the system 12 to assumethe ‘on’ condition and the DC mode.

When the LSP control system 12 is initially switched on by means of theLSP selector button 172, the LSP control system 12 assumes the DC mode.

If whilst in DC mode the ‘set +’ button 174 is pressed, the LSP controlsystem 12 sets the value of LSP_set-speed to the instant value ofvehicle speed according to vehicle speed signal 36 (FIG. 4, discussed inmore detail below) and assumes the active mode. If the vehicle speed isabove 30 kph, being the maximum allowable value of LSP_set-speed, theLSP control system 12 remains in the DC mode and ignores the request toassume the active mode. A signal may be provided to the driverindicating that the LSP control system 12 cannot be activated due to thevehicle speed exceeding the maximum allowable value of LSP_set-speed.The signal may be provided by means of a text message provided on theLSP control HMI 18, by means of an indicator lamp, an audible alert orany other suitable means.

If the resume button 173R is depressed whilst in the DC mode, the LSPcontrol system assumes the active mode provided a value of LSP_set-speedhas been set in a memory of the LSP control system 12 since the LSPcontrol system last assumed the on condition (i.e. the LSP controlsystem 12 was last switched on), and the vehicle speed does not exceed30 kph. If no value of LSP_set-speed has been set since the LSP controlsystem 12 was last switched on, the LSP control system 12 remains in theDC mode. A signal may be provided to the driver indicating that the LSPcontrol system 12 cannot be activated due to no value of LSP_set-speedhaving been set. The signal may be provided by means of a text messageprovided on the LSP control HMI 18, by means of an indicator lamp, anaudible alert or any other suitable means.

If a value of LSP_set-speed has been set since the LSP control system 12was last switched on and the resume button 173R is pressed, then ifvehicle speed is above 30 kph but less than or substantially equal to 50kph when the resume button 173R is pressed the LSP control system 12remains in the DC mode until vehicle speed falls below 30 kph. In the DCmode, provided the driver does not depress the accelerator pedal 161 theLSP control system 12 deploys the braking system 22 to slow the vehicle100 to a value of set-speed corresponding to the value of parameterLSP_set-speed. Once the vehicle speed falls to 30 kph or below, the LSPcontrol system 12 assumes the active mode in which it is operable toapply positive drive torque via the powertrain 129, as well as negativetorque via the powertrain 129 (via engine braking) and brake torque viathe braking system 22 in order to control the vehicle in accordance withthe LSP_set-speed value.

With the LSP control system 12 in the active mode, the user may increaseor decrease the value of LSP_set-speed by means of the ‘+’ and ‘−’buttons 174, 175. In addition, the user may optionally also increase ordecrease the value of LSP_(—) set-speed by lightly pressing theaccelerator or brake pedals 161, 163 respectively. In some embodiments,with the LSP control system 12 in the active mode the ‘+’ and ‘−’buttons 174, 175 may be disabled such that adjustment of the value ofLSP_set-speed can only be made by means of the accelerator and brakepedals 161, 163. This latter feature may prevent unintentional changesin set-speed from occurring, for example due to accidental pressing ofone of the ‘+’ or ‘−’ buttons 174, 175. Accidental pressing may occurfor example when negotiating difficult terrain where relatively largeand frequent changes in steering angle may be required. Otherarrangements are also useful.

It is to be understood that in the present embodiment the LSP controlsystem 12 is operable to cause the vehicle to travel in accordance witha value of set-speed in the range from 2-30 kph whilst the cruisecontrol system is operable to cause the vehicle to travel in accordancewith a value of set-speed in the range from 25-150 kph although othervalues are also useful, such as 30-120 kph or any other suitable rangeof values.

It is to be understood that if the LSP control system 12 is in theactive mode, operation of the cruise control system 16 is inhibited. Thetwo speed control systems 12, 16 therefore operate independently of oneanother, so that only one can be operable at any one time.

In some embodiments, the cruise control HMI 18 and the LSP control HMI20 may be configured within the same hardware so that, for example, thespeed selection is input via the same hardware, with one or moreseparate switches being provided to switch between the LSP control HMI20 and the cruise control HMI 18.

When in the active mode, the LSP control system 12 is configured tocommand application of positive powertrain torque and negative braketorque, as required, by transmitting a request for (positive) drivetorque in the form of a powertrain torque signal and/or a request for(negative) brake torque in the form of a brake torque signal to thebrake controller 13. The brake controller 13 arbitrates any demand forpositive powertrain torque, determining whether the request for positivepowertrain torque is allowable. If a request for positive powertraintorque is allowable the brake controller 13 issues the request to thepowertrain controller 11. In some embodiments, the request for braketorque may correspond to an amount of brake torque (or brake fluidpressure) to be developed by the braking system 22. In some alternativeembodiments the request for brake torque may be for an amount ofnegative torque to be applied to one or more wheels. The brakecontroller 13 may in some embodiments determined whether the requestednegative torque is to be supplied by means of powertrain braking alone,for example engine overrun braking, by means of powertrain braking andbrake torque developed by the braking system 22, or by means of thebraking system 22 alone. In some embodiments the brake controller 13 orLSP control system 12 may be configured to cause a required amount ofnet negative torque to be applied to one or more wheels by applyingnegative torque by means of the braking system 22 against positive drivetorque generated by the powertrain 129. Application of positive drivetorque generated by means of the powertrain 129 against negative braketorque generated by means of the braking system 22 may be made in orderto reduce wheel flare when driving on surfaces of relatively low surfacecoefficient of friction such as during off-road driving. By wheel flareis meant excessive wheel slip as a result of the application of excesspositive net torque to a wheel.

In the present embodiment the brake controller 13 also receives from theLSP control system 12 a signal S_mode indicative of the mode in whichthe LSP control system 12 is operating, i.e. whether the LSP controlsystem 12 is operating in the active mode, DC mode, standby mode or offmode.

If the brake controller 13 receives a signal S_mode indicating that theLSP control system 12 is operating in the DC mode, standby mode or offmode, the brake controller 13 sets a powertrain torque request inhibitflag in a memory thereof. The powertrain torque request inhibit flagindicates that positive torque requests to the powertrain controller 11from the brake controller 13 in response to positive torque requestsfrom the LSP control system 12 are forbidden. Accordingly, if a requestfor positive powertrain torque is received by the brake controller 13from the LSP control system 12 whilst the LSP control system 12 isoperating in the DC mode, standby mode or off mode, the positive torquerequest is ignored by the brake controller 13.

In some embodiments, the powertrain controller 11 is also provided withsignal S_mode indicating the mode in which the LSP control system 12 isoperating. If the LSP control system 12 is operating in a mode otherthan the active mode, such as the DC mode, standby mode or off mode,positive powertrain torque requests received as a consequence of acommand from the LSP control system 12 are ignored by the powertraincontroller 11.

In some embodiments, if the powertrain controller 11 receives a requestfor positive powertrain torque from the brake controller 13 as aconsequence of a command from the LSP control system 12 and the requestis received more than a predetermined period after the LSP controlsystem 12 has transitioned to a mode other than the active mode, thepowertrain controller 11 causes the LSP control system 12 to assume adisabled off mode. In the disabled off mode the LSP control system 12 iseffectively locked into the off condition or mode for the remainder ofthe current key cycle and the LSP control system 12 does not assume theDC mode in response to pressing of the LSP selector button 172. Thepredetermined period may be any suitable period such as 50 ms, 100 ms,500 ms, 1000 ms or any other suitable period. The period may be set to avalue such that any delay in receipt of a positive torque request issuedby the LSP control system 12 immediately prior to a transition from theactive mode to a mode other than the active mode (and in which positivetorque requests are not permitted) that is consistent with normal systemoperation will not trigger a transition to the disabled off mode.However, the powertrain controller 11 is configured such that anyrequest for positive powertrain torque received by the powertraincontroller 11 as a consequence of a request issued by the LSP controlsystem 12 after assuming a mode other than the active mode (and in whichpositive torque requests are not permitted) will trigger a transition tothe disabled off mode.

It is to be understood that other arrangements may also be useful. Forexample, in some embodiments, in the disabled off mode the LSP controlsystem 12 may be configured not to respond to the LSP selector button172 by assuming the DC mode until after the vehicle has transitionedfrom power mode PM7 to power mode PM4. As described above, a transitionfrom power mode PM7 to power mode PM4 may be accomplished by depressingthe start/stop button 124S. When the vehicle 100 is subsequentlyrestarted and assumes power mode PM7, the LSP control system 12 may bepermitted to assume operation in the active mode as required.

It is to be understood that some vehicles may be provided with knownautomatic engine stop/start functionality. In vehicles with thisfunctionality, the powertrain controller 11 is configured to commandstopping and starting of the engine 121 according to a stop/startcontrol methodology when the vehicle 100 is being held stationary bymeans of brake pedal 163 with the transmission in the drive mode D. Theprocess of automatically commanding stopping and restarting of theengine 121 may be referred to as an automatic stop/start cycle. Invehicles having automatic engine stop/start functionality, thecontroller 10 may be configured to cause the vehicle 100 to assume apower mode PM6A when the engine 121 is stopped during a stop/startcycle. Power mode PM6A is similar to power mode 6, except that disablingof certain vehicle systems such as the infotainment system is notperformed when in power mode PM6A. In power mode PM6A, the powertraincontroller 11 is configured to restart the engine 121 upon receipt of asignal indicating a user has released the brake pedal 163. It is to beunderstood that in some embodiments, a vehicle 100 may be configured torequire an engine restart before the LSP control system 12 may exit theDC fault mode but an engine restart as part of an automatic stop/startcycle may be configured not to qualify as an engine restart permittingthe system 12 to exit the DC fault mode. In some embodiments therefore,a transition from power mode PM7 to power mode PM6A and back to powermode PM7 does not permit the LSP control system 12 to exit the disabledoff mode.

In some embodiments the LSP control system 12 may be configured suchthat it can assume one of a number of different further modes such as:

(i) DC fault mode

(ii) DC fault mode fade-out mode

(iii) DC mode fade-out mode

(iv) Active standby mode

(v) DC standby mode

The DC fault mode corresponds to the DC mode except that if the DC faultmode is assumed by the LSP control system 12, the LSP control system 12is unable subsequently to assume the active mode for the remainder ofthe current key cycle. Thus, when the next key-on procedure isperformed, following the next key-off procedure, the LSP control system12 is permitted to assume the active mode when required. The vehicle 100may be configured wherein the LSP control system 12 may assume the DCfault mode if a fault is detected indicating that the LSP control system12 should not be permitted to request positive powertrain drive torquebut where it is determined that it may be desirable for the benefits ofDC mode to be enjoyed. Thus a transition from active mode to DC faultmode may be preferable to a transition to the off mode, particularlywhen negotiating off road conditions, in the event of a relatively minorfault in respect of the LSP control system 12.

In some embodiments, if a transition to DC fault mode occurs with morethan a predetermined frequency, the LSP control system 12 may becomelatched in the DC fault mode until a reset procedure is performedrequiring action other than a key-off and subsequent key-on procedure inorder to permit the active mode to be assumed again. In someembodiments, the LSP control system 12 may require a predetermined codeto be provided to it. In some embodiments, the LSP control system 12 maybe configured to receive the code via a computing device external to thevehicle 100 that temporarily communicates with the LSP control system 12in order to provide the code. The computing device may be a devicemaintained by a vehicle servicing organisation such as a dealercertified by a manufacturer of the vehicle 100. The computing device maybe in the form of a laptop or other computing device, and be configuredto communicate wirelessly with the LSP control system 12 or via a wiredconnection.

The predetermined frequency may be defined in terms of a predeterminednumber of occurrences in a predetermined number of key cycles, or apredetermined distance driven, or be time based such as a predeterminednumber of occurrences in a predetermined period in which the vehicle isin power mode 7 (or power mode 6A in addition to power mode 7, in thecase of a vehicle with stop/start functionality) over one or more keycycles, or a predetermined number of occurrences in a given calendarperiod, such as a day, a week, a month or any other suitable frequency.

The DC fault mode fade-out mode is a mode assumed by the LSP controlsystem 12 when transitioning from the DC fault mode to an off mode suchas disabled off, unless an immediate (‘binary’) transition to an offmode is required in which case the DC fault mode fade-out mode is notassumed. Thus, under certain conditions, rather than abruptly terminatecommanding application of brake torque by means of the braking system 22when ceasing operation in the DC fault mode and transitioning to an offmode such as ‘off’ or ‘disabled off’, the LSP control system 12gradually fades out the application of any brake torque applied by thebraking system 22 as a consequence of being in the DC fault mode, beforeassuming the off or disabled off mode. This is at least in part so as toallow a driver time to adapt to driving without the system 12 applyingbrake torque automatically.

Similarly, if the LSP control system 12 transitions from the DC mode toa mode in which the LSP control system 12 is unable to commandapplication of brake torque such as the standby mode, off mode ordisabled off mode, the LSP control system 12 may assume the DC fade-outmode as an intermediate mode. In the DC fade-out mode, like the DC faultmode fade-out mode, the LSP control system 12 gradually reduces theamount of any brake torque commanded by the LSP control system 12,before assuming the target mode such as standby mode, off mode ordisabled off mode.

The active standby mode is a mode assumed by the LSP control system 12from the active mode if the driver over-rides the LSP control system 12by depressing the accelerator pedal 161 to increase vehicle speed. Ifthe driver subsequently releases the accelerator pedal with vehiclespeed within the allowable range for the LSP control system 12 tooperate in the active mode (i.e. a speed in the range 2-30 kph), the LSPcontrol system 12 resumes operation in the active mode.

The DC standby mode is a mode assumed by the LSP control system 12 ifwhilst operating in the DC mode the driver over-rides the LSP controlsystem 12 by depressing the accelerator pedal 161. If the driversubsequently releases the accelerator pedal, then when vehicle speed iswithin the allowable range for the LSP control system 12 to operate inthe DC mode (i.e. a speed in the range 2-30 kph), the LSP control system12 resumes operation in the DC mode. Other arrangements are also useful.In some embodiments the LSP control system 12 may be configured toassume DC mode from the DC standby mode and cause application of braketorque to slow the vehicle 100 when a driver releases the acceleratorpedal 161 even at speeds above 30 kph. In some embodiments the LSPcontrol system 12 may be configured to cause application of brake torqueat speeds of up to 50 kph, 80 kph or any other suitable speed in orderto cause vehicle speed to reduce to the LSP target speed LSP_set-speed.The LSP control system 12 may be configured to take into accountnegative torque applied by a powertrain due for example to engineover-run braking in determining an amount of brake torque required inorder to cause a vehicle to slow at a desired rate. The LSP controlsystem 12 may be configured to cause a vehicle to slow at a desired rateaccording to a predetermined deceleration profile.

In some embodiments, if the powertrain controller 11 receives a requestfor positive powertrain torque from the brake controller 13 as aconsequence of a command from the LSP control system 12 and the LSPcontrol system 12 is in the DC mode, the powertrain controller 11 causesthe LSP control system 12 to assume the DC fault mode if the positivetorque request is received more than a predetermined period after theLSP control system 12 has transitioned to the DC mode. As noted above,in the DC fault mode the LSP control system 12 is permitted to causeapplication of brake torque by the braking system 22 to control vehiclespeed but is prevented from assuming the active or FF mode for theremainder of the current key cycle. In these circumstances, the LSPcontrol system 12 assumes the DC fault mode substantially immediatelywith no requirement to blend the transition between the DC mode and DCfault mode.

As noted above, the predetermined period may be any suitable period suchas 50 ms, 100 ms, 500 ms, 1000 ms or any other suitable period. Theperiod may be set to a value such that any inherent system delay inreceipt by the powertrain controller 11 of a torque request from thebrake controller 13 as a consequence of a request issued by the LSPcontrol system 12 prior to a transition from the active mode to the DCmode will not trigger a transition to the DC fault mode. It is to beunderstood that by inherent system delay is meant a delay in signalreceipt that occurs during normal operation, for example due to arequirement to synchronise timing signals, or to transmit commands fromthe LSP control system 12 to the powertrain controller 11 atpredetermined intervals as part of an inter-controller communicationsprotocol.

In some embodiments, if the powertrain controller 11 receives a requestfor positive powertrain torque from the brake controller 13 as aconsequence of a command from the LSP control system 12 and the LSPcontrol system 12 is in the DC fault mode or DC fault mode fade out modeonly, the powertrain controller 11 causes the LSP control system 12 toassume the disabled off mode if the positive torque request is receivedmore than a predetermined period after the LSP control system 12 hastransitioned to the DC fault mode or DC fault mode fade out mode. In thepresent embodiment the predetermined period is a period of 500 ms.However the predetermined period may be any suitable period such as 50ms, 100 ms, 1000 ms or any other suitable period. The LSP control system12 may be configured substantially abruptly to terminate application ofany negative (brake) torque requested by the LSP control system 12 whenthe transition to the disabled off mode is commanded even if the system12 is in the processes of fading out any negative brake torque that isbeing applied as a result of a request issued by the LSP control system12

In some embodiments, in addition or instead, if the powertraincontroller 11 receives a request for positive powertrain torque from thebrake controller 13 as a consequence of a command from the LSP controlsystem 12 and the signal S_mode indicates that the LSP control system 12is in the DC mode, DC standby mode, DC mode fade-out mode or activestandby mode, the powertrain controller 11 causes the LSP control system12 to assume the disabled off mode if the positive torque request isreceived over a sustained period of more than a predetermined period. Inthe present embodiment the predetermined period is substantially 500 ms.However the predetermined period may be any suitable period such as 100ms, 1000 ms or any other suitable period. The LSP control system 12 isconfigured gradually to cause fade-out of any negative (brake) torquebeing applied as a consequence of a command from the LSP control system12 when the transition to the disabled off mode is commanded. Thefade-out of brake torque may be accomplished by assuming the DC modefade-out mode or DC fault mode fade-out mode if they have not alreadybeen assumed.

In some embodiments, the LSP control system 12 is caused to assume thedisabled off mode if the powertrain controller 11 receives a request forpositive powertrain torque from the brake controller 13 as a consequenceof a command from the LSP control system 12 and signal S_mode indicatesthat the LSP control system 12 is in the DC fault mode or DC fault modefade-out mode, as well as when the signal indicates the LSP controlsystem 12 is in the DC mode, DC standby mode, DC mode fade-out mode oractive standby mode.

It is to be understood that in some embodiments, instead of graduallyfading out negative brake torque, the LSP control system 12 may beconfigured to abruptly terminate application of any negative braketorque as a consequence of a command by the LSP control system 12. Thus,if a request for positive powertrain torque is received over a sustainedperiod of more than the predetermined period when the LSP control system12 is in the DC mode, DC standby mode, DC fault mode, DC mode fade-outmode, DC fault mode fade-out mode or active standby mode the system mayabruptly terminate application of brake torque caused by the LSP controlsystem 12. It is to be understood that the braking system 12 continuesto respond to driver brake commands via the brake pedal 163.

It is to be understood that in the present embodiment if a driverswitches off the LSP control system 12 manually, the LSP control system12 is configured gradually to cause fade-out of any negative (brake)torque being applied as a consequence of a command from the LSP controlsystem 12. This feature has the advantage that vehicle composure may beenhanced.

FIG. 4 illustrates the means by which vehicle speed is controlled in theLSP control system 12. As described above, a speed selected by a user(set-speed) is input to the LSP control system 12 via the LSP controlHMI 20. A vehicle speed calculator 34 provides a vehicle speed signal 36indicative of vehicle speed to the LSP control system 12. The speedcalculator 34 determines vehicle speed based on wheel speed signalsprovided by wheel speed sensors 111S, 112S, 114S, 115S. The LSP controlsystem 12 includes a comparator 28 which compares the LSP control systemset-speed LSP_set-speed 38 (also referred to as a ‘target speed’ 38)selected by the user with the measured speed 36 and provides an outputsignal 30 indicative of the comparison. The output signal 30 is providedto an evaluator unit 40 of the VCU 10 which interprets the output signal30 as either a demand for additional torque to be applied to the vehiclewheels 111-115, or for a reduction in torque applied to the vehiclewheels 111-115, depending on whether the vehicle speed needs to beincreased or decreased to maintain the speed LSP_set-speed. An increasein torque is generally accomplished by increasing the amount ofpowertrain torque delivered to a given position of the powertrain, forexample an engine output shaft, a wheel or any other suitable location.A decrease in torque at a given wheel to a value that is less positiveor more negative may be accomplished by decreasing the amount of anypositive powertrain torque delivered to a wheel, by increasing theamount of any negative powertrain torque delivered to a wheel, forexample by reducing an amount of air and/or fuel supplied to an engine121, and/or by increasing a braking force on a wheel. It is to beunderstood that in some embodiments in which a powertrain 129 has one ormore electric machines operable as a generator, negative torque may beapplied by the powertrain 129 to one or more wheels by means of theelectric machine. As noted above negative torque may also be applied bymeans of engine braking in some circumstances, depending at least inpart on the speed at which the vehicle 100 is moving. If one or moreelectric machines are provided that are operable as propulsion motors,positive drive torque may be applied by means of the one or moreelectric machines.

An output 42 from the evaluator unit 40 is provided to the brakecontroller 13. The brake controller 13 in turn controls a net torqueapplied to the vehicle wheels 111-115 by commanding application of braketorque via the brakes 111B, 112B, 114B, 115B and/or positive drivetorque by commanding powertrain controller 11 to deliver a requiredamount of powertrain torque. The net torque may be increased ordecreased depending on whether the evaluator unit 40 demands positive ornegative torque. In order to cause application of the necessary positiveor negative torque to the wheels, the brake controller 13 may commandthat positive or negative torque is applied to the vehicle wheels by thepowertrain 129 and/or that a braking force is applied to the vehiclewheels by the braking system 22, either or both of which may be used toimplement the change in torque that is necessary to attain and maintaina required vehicle speed. In the illustrated embodiment the torque isapplied to the vehicle wheels individually so as to maintain the vehicle100 at the required speed, but in another embodiment torque may beapplied to the wheels collectively to maintain the required speed. Insome embodiments, the powertrain controller 11 may be operable tocontrol an amount of torque applied to one or more wheels at least inpart by controlling a driveline component such as a rear drive unit,front drive unit, differential or any other suitable component. Forexample, one or more components of the driveline 130 may include one ormore clutches operable to allow an amount of torque applied to wheels ofa given axle to be controlled independently of the torque applied towheels of another axle, and/or the amount of torque applied to one ormore individual wheels to be controlled independently of other wheels.Other arrangements are also useful.

Where a powertrain 129 includes one or more electric machines, forexample one or more propulsion motors and/or generators, the powertraincontroller 11 may be operable to modulate or control the amount oftorque applied to one or more wheels at least in part by means of theone or more electric machines.

The LSP control system 12 also receives a signal 48 indicative of awheel slip event having occurred. This may be the same signal 48 that issupplied to the on-highway cruise control system 16 of the vehicle, andwhich in the case of the latter triggers an override or inhibit mode ofoperation of the on-highway cruise control system 16 so that automaticcontrol of vehicle speed by the on-highway cruise control system 16 issuspended or cancelled. However, the LSP control system 12 is notarranged to cancel or suspend operation in dependence on receipt of awheel slip signal 48 indicative of wheel slip. Rather, the system 12 isarranged to monitor and subsequently manage wheel slip so as to reducedriver workload. During a slip event, the LSP control system 12continues to compare the measured vehicle speed with the value ofLSP_set-speed, and continues to control automatically the torque appliedto the vehicle wheels so as to maintain vehicle speed at the selectedvalue. It is to be understood therefore that the LSP control system 12is configured differently to the cruise control system 16, for which awheel slip event has the effect of overriding the cruise controlfunction so that manual operation of the vehicle 100 must be resumed, orspeed control by the cruise control system 12 resumed by pressing theresume button 173R or set-speed button 173.

In a further embodiment of the present invention (not shown) a wheelslip signal 48 is derived not just from a comparison of wheel speeds,but further refined using sensor data indicative of the vehicle's speedover ground. Such a speed over ground determination may be made viaglobal positioning (GPS) data, or via a vehicle mounted radar or laserbased system arranged to determine the relative movement of the vehicle100 and the ground over which it is travelling. A camera system may beemployed for determining speed over ground in some embodiments.

At any stage of the LSP control process the user can override the LSPfunction by depressing the accelerator pedal 161 and/or brake pedal 163to adjust the vehicle speed in a positive or negative sense. However,absent any override by a user, in the event that a wheel slip event isdetected via signal 48, the LSP control system 12 remains active andcontrol of vehicle speed by the LSP control system 12 is not terminated.As shown in FIG. 4, this may be implemented by providing a wheel slipevent signal 48 to the LSP control system 12 which is then managed bythe LSP control system 12 and/or brake controller 13. In the embodimentshown in FIG. 1 the SCS 14S generates the wheel slip event signal 48 andsupplies it to the LSP control system 12 and cruise control system 16.

A wheel slip event is triggered when a loss of traction occurs at anyone of the vehicle wheels. Wheels and tyres may be more prone to losingtraction when travelling for example on snow, ice, mud or sand and/or onsteep gradients or cross-slopes. A vehicle 100 may also be more prone tolosing traction in environments where the terrain is more uneven orslippery compared with driving on a highway in normal on-roadconditions. Embodiments of the present invention therefore findparticular benefit when the vehicle 100 is being driven in an off-roadenvironment, or in conditions in which wheel slip may commonly occur.Manual operation in such conditions can be a difficult and oftenstressful experience for the driver and may result in an uncomfortableride.

The vehicle 100 is also provided with additional sensors (not shown)which are representative of a variety of different parameters associatedwith vehicle motion and status. The signals from the sensors provide, orare used to calculate, a plurality of driving condition indicators (alsoreferred to as terrain indicators) which are indicative of the nature ofthe terrain conditions over which the vehicle is travelling. Suitablesensor data may be provided by inertial systems unique to the LSP or HDCcontrol system 12, 12HD or systems that form part of another vehiclesub-system such as an occupant restraint system or any other sub-systemwhich may provide data from sensors such as gyros and/or accelerometersthat may be indicative of vehicle body movement and may provide a usefulinput to the LSP and/or HDC control systems 12, 12HD.

The sensors on the vehicle 100 include sensors which provide continuoussensor outputs to the VCU 10, including wheel speed sensors, asmentioned previously and as shown in FIG. 1, and other sensors (notshown) such as an ambient temperature sensor, an atmospheric pressuresensor, tyre pressure sensors, wheel articulation sensors, gyroscopicsensors to detect vehicular yaw, roll and pitch angle and rate, avehicle speed sensor, a longitudinal acceleration sensor, an enginetorque sensor (or engine torque estimator), a steering angle sensor, asteering wheel speed sensor, a gradient sensor (or gradient estimator),a lateral acceleration sensor which may be part of the SCS 14S, a brakepedal position sensor, a brake pressure sensor, an accelerator pedalposition sensor, longitudinal, lateral and vertical motion sensors, andwater detection sensors forming part of a vehicle wading assistancesystem (not shown). In other embodiments, only a selection of theaforementioned sensors may be used. Other sensors may be useful inaddition or instead in some embodiments.

The VCU 10 also receives a signal from the steering controller 170C. Thesteering controller 170C is in the form of an electronic power assistedsteering unit (ePAS unit). The steering controller 170C provides asignal to the VCU 10 indicative of the steering force being applied tosteerable road wheels 111, 112 of the vehicle 100. This forcecorresponds to that applied by a user to the steering wheel 171 incombination with steering force generated by the ePAS unit 170C.

The VCU 10 evaluates the various sensor inputs to determine theprobability that each of a plurality of different control modes (drivingmodes) for the vehicle subsystems is appropriate, with each control modecorresponding to a particular terrain type over which the vehicle istravelling (for example, mud and ruts, sand, grass/gravel/snow).

If the user has selected operation of the vehicle in an automaticdriving mode selection condition, the VCU 10 then selects the mostappropriate one of the control modes and is configured automatically tocontrol the subsystems according to the selected mode. This aspect ofthe invention is described in further detail in our co-pending patentapplication nos. GB2492748, GB2492655 and GB2499252, the contents ofeach of which is incorporated herein by reference.

The nature of the terrain over which the vehicle is travelling (asdetermined by reference to the selected control mode) may also beutilised in the LSP control system 12 to determine an appropriateincrease or decrease in vehicle speed. For example, if the user selectsa value of LSP_set-speed that is not suitable for the nature of theterrain over which the vehicle is travelling, the system 12 is operableto automatically adjust the vehicle speed downwards by reducing thespeed of the vehicle wheels. In some cases, for example, the userselected speed may not be achievable or appropriate over certain terraintypes, particularly in the case of uneven or rough surfaces. If thesystem 12 selects a set-speed that differs from the user-selectedset-speed, a visual indication of the speed constraint is provided tothe user via the LSP HMI 20 to indicate that an alternative speed hasbeen adopted.

It is to be understood that the values of speed referred to herein, suchas the range of speeds over which the LSP control system 12 is permittedto operate in the active mode, refer to the values of speed displayed ona speedometer viewed by a driver whilst driving the vehicle 100. It isto be understood that in some embodiments the value of speed displayedon a speedometer presented to a driver may be arranged to be greaterthan an absolute speed of a vehicle 100 over ground, for example asdetermined by reference to vehicle wheel speed or other means formeasuring speed over ground.

As described above, the vehicle 100 has a cruise control system 16 and aHDC system 12HD configured to cause the vehicle 100 to operate inaccordance with respective set-speed values cruise_set-speed,HDC_set-speed. The VCU 10 is configured wherein when the LSP controlsystem 12 is in an on mode, the cruise control system 16 and the HDCcontrol system 12HD remain in an off mode even if a user depresses thecruise control system selector button 176 or HDC system selector button177. Thus, neither the cruise control system 16 nor the HDC controlsystem 12HD may assume an on mode when the LSP control system 12 is inan on mode. In the present embodiment, the VCU 10 broadcasts a signalS_mode having a value indicative of the mode in which the LSP controlsystem 12 is currently operating. The signal S_mode may be in the formof a value of a parameter that is transmitted digitally to the brakecontroller 13 and powertrain controller 11, for example by means of acontroller area network (CAN) bus, and optionally one or more othercontrollers in some embodiments.

In some embodiments, the cruise control system 16 and HDC system 12HDmay be configured to monitor the signal S_mode. The cruise controlsystem 16 and HDC system 12HD may be configured to remain in the offmode and not to assume an on mode if the signal S_mode indicates thatthe LSP control system 12 is in an on mode. Thus in some embodiments thecruise control system 16 and HDC system 12HD may be configured tomonitor the signal S_mode even when the systems 16, 12HD are in the offmode.

In the some embodiments, the cruise control system 16 may be providedwith active or adaptive cruise control functionality. In suchembodiments, when the cruise control system 16 is in an on mode thesystem 16 is configured to receive data indicative of a distance or timegap between the vehicle 100 and a followed vehicle being a vehicle aheadof the vehicle 100 travelling in the same direction. The data may bereceived from a radar module fitted to the vehicle 100. The radar modulemay measure time of flight of a radar signal reflected from a vehicleahead and therefore determine either an actual distance separation ofthe vehicles or a time separation of the vehicles. The cruise controlsystem 16 may be configured to adjust the speed of the vehicle 100 inorder to maintain a distance or time gap behind the followed vehicle ata value not less than a predetermined following distance, distancefollow. As used herein the term distance_follow refers to either anactual distance (i.e. a set distance) or a time gap (i.e. a speedvariable distance). The value of distance_follow may be speed dependentand/or adjustable by a driver of the vehicle 100. The cruise controlsystem 16 maygenerates a powertrain control signal and a brake controlsignal that cause the powertrain 129 and braking system 22 to generaterespective amounts of powertrain torque and brake torque to cause thevehicle to maintain a speed substantially equal to cruise_set-speedsubject to the distance obehind a followed vehicle or time gap being notless than distance_follow.

Furthermore, in some embodiments the vehicle 100 may be provided with aqueue assist (QA) control system. The QA control system may beconfigured to generate a powertrain control signal and a brake controlsignal that cause the powertrain 129 and braking system 22 to generaterespective amounts of powertrain torque and brake torque to cause thevehicle to maintain a suitable distance behind a followed vehicle inqueuing traffic. Thus the QA control system is configured to cause thevehicle to accelerate from rest and slow to a halt in queuing traffic.The QA system may be configured to cause the vehicle 100 to maintain adistance behind a followed vehicle that is dependent on speed of thevehicle 100, the distance increasing with increasing vehicle speed. Insome embodiments, the QA control system may be prevented from generatingthe powertrain control signal and brake control signal when the LSPcontrol system 12 is in an on mode. Optionally, the QA control systemmay be prevented from assuming an on mode when the LSP control system 12is in an on mode. Other arrangements are also useful.

As described above, in some embodiments the vehicle 100 may be providedwith stop/start functionality. In some embodiments, the stop/startfunctionality may be disabled when the LSP control system 12 is in an oncondition.

It is to be understood that the disabled off mode of the LSP controlsystem 12 may also be considered to be an off mode.

In some embodiments, operation of a cruise control system 16 with orwithout active cruise functionality, an HDC control system 12HD andoptionally a QA control system may be prevented when the LSP controlsystem 12 is in an on mode and the vehicle speed is less than apredetermined value such as a maximum speed in which the LSP controlsystem may assume an on mode. For example, in some embodiments if theLSP control system 12 is in an on mode and vehicle speed exceeds 30 kph,the LSP control system 12 assumes the standby mode, being an on mode.However if vehicle speed subsequently exceeds an upper speed limit forthe LSP control system 12 to remain in the standby mode, the LSP controlsystem may assume the off mode. Once the LSP control system 12 is in theoff mode the cruise control system 16 may assume an on mode absent anyconditions preventing the cruise control system 16 from assuming the onmode.

In the present embodiment, when the LSP control system 12 is switchedon, any stored value or values of cruise_set-speed and HDC_set-speed areerased. In some embodiments the values are erased by setting the valueof parameters cruise_set-speed and HDC_set-speed to correspond to analphanumeric word such as ‘RESET’ or ‘NULL’ as opposed to valuescorresponding to speeds. As a consequence, when the LSP control systemis active a risk that pressing of the resume button 173R causes thevalue of LSP_set-speed to be set to a value of a set-speed set by aspeed control system other than the LSP control system 12 is reduced.

In some embodiments the VCU 10 may be configured to store a mostrecently used value of respective set-speed value LSP_set-speed,cruise_set-speed, HDC_set-speed used by LSP control system 12, cruisecontrol system 16 and HDC control system 12HD in a memory that is notaccessible to the systems 12, 16, 12HD. The value may be recalled by theVCU 10 and provided to the respective speed control system 12, 16, 12HDaccording to a predetermined procedure to allow a user to employ apreviously used set-speed in one system 12, 16, 12HD after another ofthe systems 12, 16, 12HD has been used. The most recently used value ofset-speed may be stored by the VCU 10 when the respective system 12, 16,12HD is switched off in some embodiments.

In some embodiments, when a given speed control system is in an on mode,the value of set-speed employed for vehicle control is stored in a firstmemory which may be a temporary memory. When the speed control system isswitched off, the most recent value of set-speed employed by that speedcontrol system may be stored in a second memory for recall at a latertime. For example, the most recent value of set-speed employed by thatspeed control system may be stored in the second memory for recall thenext time that speed control system is activated. Thus, in use the HDCcontrol system 12HD may store a current value of HDC_set-speed in afirst memory of the VCU 10. If the HDC control system 12HD issubsequently switched off, the VCU 10 may be configured to store themost recent value of HDC_set-speed in a second memory of the VCU 10.When the HDC control system 12HD is subsequently switch on again, theVCU 10 may be configured to copy the value of HDC_set-speed stored inthe second memory to the first memory for use by the HDC control system12 if required. Other arrangements are also useful.

It is to be understood that in vehicles having other speed controlsystems in addition to or instead of a cruise control system 16 and/orHDC control system 12HD, one or more values of set-speed associated withthose systems may also be erased from memory, or transferred from afirst memory to a second memory, when the speed control system assumesthe off mode.

FIG. 7 illustrates a method of operation of a vehicle 100 according toan embodiment of the present invention.

At step S101 the VCU 10 checks whether the LSP control system 12 is inan on mode. If the LSP control system 12 is in an on mode the methodcontinues at step S103 else step S101 is repeated.

At step S103 the VCU 10 checks whether the LSP selector button 172 hasbeen pressed. If the button 172 has been pressed the method continues atstep S105 else the method continues at step S101.

At step S105 the LSP control system 12 sets the value of LSP_set-speedto RESET and continues at step S107.

At step S107 the LSP control system 12 assumes the off mode.

At step S109 the method terminates.

FIG. 8 illustrates a further method of operation of a vehicle 100according to an embodiment of the invention.

At step S101 the VCU 10 determines whether the cruise control system 16is in an on mode.

If the system 16 is in an on mode the method continues at step S103 elsestep S101 repeats.

At step S103 the VCU 10 determines whether the LSP selector button 172has been pressed. If the button 172 has been pressed the methodcontinues at step S105 else the method continues at step S101.

At step S105 the VCU 10 determines whether the cruise control system 16is causing the braking system 22 to be applied. If the cruise controlsystem 16 is causing the braking system 22 to be applied the methodcontinues at step S101 else the method continues at step S107.

At step S107 the cruise control system 16 sets the value ofcruise_set-speed to RESET and continues at step S109.

At step S109 the VCU 10 causes the cruise control system 16 to assumethe off mode.

At step 5111 the VCU 10 causes the LSP control system 12 to assume an onmode, in the present embodiment the DC mode.

At step S113 the method terminates.

FIG. 9 illustrates a further method of operation of a vehicle 100according to an embodiment of the invention.

At step S101 the VCU 10 determines whether the HDC control system 12HDis in an on mode. If the system 12HD is in an on mode the methodcontinues at step S103 else step S101 repeats.

At step S103 the VCU 10 determines whether the LSP selector button 172has been pressed. If the button 172 has been pressed the methodcontinues at step S105 else the method continues at step S101.

At step S105 the VCU 10 determines whether the HDC control system 12HDis causing the braking system 22 to be applied. If the HDC controlsystem 12HD is causing the braking system 22 to be applied the methodcontinues at step S101 else the method continues at step S107.

At step S107 the HDC control system 12HD sets the value of HDC_set-speedto RESET and continues at step S109.

At step S109 the VCU 10 causes the HDC control system 12HD to assume theoff mode.

At step 5111 the VCU 10 causes the LSP control system 12 to assume an onmode, in the present embodiment the DC mode.

At step S113 the method terminates.

In the present embodiment, the VCU 10 is configured to permit the LSPcontrol system 12 to assume an on state if the LSP selector button 172is pressed and the cruise control system 16 is in an on mode. Asdescribed above, in this case the cruise control system 16 is caused toassume the off mode prior to the LSP control system 12 assuming the onmode. However, if the cruise control system 16 is actively causingbraking when the LSP control system selector button 172 is pressed, theLSP control system 12 is not permitted to assume the on mode until thecruise control system 16 has stopped causing a brake to be applied. Insome embodiments, the LSP control system 12 may automatically assume anon mode, in some embodiments the DC mode, once the cruise control system16 has stopped causing a brake to be applied if the LSP control systemselector button 172 is pressed whilst the cruise control system 16 iscausing a brake to be applied. In some embodiments the cruise controlsystem 16 may be configured to cause a brake to be applied only if thecruise control system 16 is operating with active cruise controlfunctionality enabled.

The vehicle 100 of FIG. 1 has a suite of active safety featuresdescribed above including anti-lock braking system (ABS) controller 13that is configured to implement a known anti-lock braking systemfunctionality in order to reduce wheel slip during braking. When thebrake controller 13 determines that wheel slip exceeds a predeterminedamount, during brake application, the brake controller 13 causes areduction in the amount of brake pressure applied by one or more brakesin order to reduce the amount of wheel slip. An event in which the brakecontroller 13 intervenes during brake application to reduce the amountof braking due to excessive wheel slip may be referred to as an ABSevent or ABS intervention event. Similarly, an event in which the SCS14S causes application of a brake to one or more wheels or the TCS 14Tcauses application of a brake to one or more wheels or a reduction inpowertrain torque at one or more wheels may be referred to an SCS or TCSintervention event.

For each of these events there are one or more associated thresholdconditions that must be met in order to trigger the event. In the caseof the ABS controller 13, an ABS intervention event is triggered whenthe vehicle 100 is travelling at a speed exceeding a predeterminedthreshold speed, in the present embodiment a speed of 5 kph, and theamount of negative wheel slip due to braking, neg_slip, exceeds apredetermined ABS slip threshold value ABS_slip_thresh due to the one ormore wheels spinning at a speed that is less than vehicle speed overground, including in the case that one or more wheels are not spinning.The predetermined threshold ABS_slip_thresh may be dependent on vehiclespeed in some embodiments, including the present embodiment.

In the case of the SCS 14S, an SCS intervention event is triggered whenthe vehicle 100 is travelling at a speed exceeding a predeterminedthreshold value and a measured rate of yaw of the vehicle 100 differsfrom an expected rate for the instant steering angle by a yaw rate errorvalue yawrate_err by more than a threshold value SCS_yawrate_err_thresh.

In the case of the TCS 14T, a TCS intervention event is triggered whenthe amount of positive slip of one or more wheels driven by thepowertrain 129 due to a wheel spinning faster than vehicle speed overground, pos_slip, exceeds a predetermined TCS slip threshold valueTCS_slip_thresh. The TCS slip_threshold may be dependent on vehiclespeed over ground in some embodiments, determined by reference to avehicle ‘reference speed’ value that is provided to each of thecontrollers of the vehicle 100.

In the present embodiment, the LSP control system 12 is configured tomonitor the values of the parameters triggering an ABS interventionevent, SCS intervention event and TCS intervention event, i.e. thevalues of neg_slip, yawrate_err and pos_slip respectively.

If the LSP control system 12 is in the active mode any of an ABSintervention event, SCS intervention event or TCS intervention event istriggered the LSP control system 12 determines whether the value of theparameter triggering the intervention event exceeds a respective firstpredetermined threshold value for that event. If the value of theparameter does exceed the first predetermined threshold value the LSPcontrol system 12 assumes the DC mode instead of the active mode.

Thus in the case of an ABS intervention event the LSP control system 12checks whether the value of neg_slip exceeds a first predeterminedthreshold value ABS_slip_thresh_1. In the case of an SCS interventionevent the LSP control system 12 checks whether the value of yawrate_errexceeds a first predetermined threshold value SCS_yawrate_err_thresh_1.In the case of a TCS intervention event the LSP control system 12 checkswhether the value of pos_slip exceeds a first predetermined thresholdvalue TCS_slip_thresh_1.

If the LSP control system 12 is in the DC mode the system 12 determineswhether the value of the parameter triggering the intervention eventexceeds a respective second predetermined threshold valueABS_slip_thresh_2, SCS_yawrate_err_thresh_2, TCS_slip_thresh_2 dependingon whether the intervention event is an ABS, SCS or TCS interventionevent. If the value of the parameter does exceed the secondpredetermined threshold value the LSP control system 12 transitions tothe off mode from the DC mode. In the present embodiment the secondpredetermined threshold values ABS_slip_thresh_2,SCS_yawrate_err_thresh_2, TCS_slip_thresh_2 are greater than thecorresponding first predetermined threshold values ABS_slip_thresh_1,SCS_yawrate_err_thresh_1, TCS_slip_thresh_1 although other arrangementsare also useful.

It is to be understood that in the present embodiment the first andsecond predetermined threshold values for each event are higher than thethreshold values triggering an ABS event, SCS event or TCS event. Thus,the occurrence of an ABS event, SCS event or TCS event will notnecessarily cause the LSP control system to transition from the activemode to the DC mode, or from the DC mode to the off mode. Thus, only inthe case the parameter triggering the intervention event, such as awheel slip value or yaw rate error value, exceeds a predeterminedthreshold value, does the LSP control system 12 transition to adifferent mode. It is to be understood that the LSP control system 12transitions to a less functional mode in each case. Thus, the DC mode isa less functional state than the active mode because the LSP controlsystem 12 cannot cause application of positive powertrain drive torquewhen in the DC mode. Similarly, the off mode is a less functional statethan the DC mode because in the off mode the LSP control system 12cannot cause application of a braking system or positive powertraindrive torque.

It is to be understood that the LSP control system 12 may in addition orinstead by configured to transition to a less functional state independence on the occurrence of one or more other torque interventionevents such as one or more other stability control events. For examplethe system 12 may transition to a less functional state in dependence ona roll stability control (RSC) intervention event in which a rollstability control system (RSC system) intervenes to cause a change in anamount of brake torque and/or powertrain torque applied to one or morewheels in response to detection of roll of the vehicle about alongitudinal axis exceeding a predetermined value. In some embodimentsthe RSC system may be configured to trigger an RSC intervention event inthe event that the rate of roll and/or the roll angle exceed respectivepredetermined values. The predetermined values may be dependent on oneor more parameters such as vehicle speed in some embodiments.

FIG. 10 illustrates a method according to an embodiment of the presentinvention. At step S101, the LSP control system 12 determines whether itis in the active mode. If it is in the active mode the method continuesat step S103 else the method continues at step S109.

At step S103 the LSP control system 12 determines whether an ABSintervention event is occurring by reference to a flag that is set whensuch as event is occurring. If an ABS intervention event is occurringthe method continues at step S105 else the method continues at stepS101.

At step S105 the LSP control system determines whether the value ofparameter neg_slip is greater than that of ABS_slip_thresh_1. If thevalue of parameter neg_slip is greater than that of ABS_slip_thresh_1the method continues at step S107 else the method continues at stepS101.

At step S107 the LSP control system 12 switches to the DC mode. Themethod then continues at step S109.

At step S109 the LSP control system 12 determines whether the LSPcontrol system 12 is in the DC mode. If the LSP control system 12 is inthe DC mode the method continues at step S111 else the method continuesat step S101.

At step S111 the LSP control system 12 determines whether an ABSintervention event is occurring. If such an event is occurring themethod continues at step S113 else the method continues at step S101.

At step S113 the LSP control system 12 determines whether the value ofneg_slip is greater than the value of ABS_slip_thresh_2. If this is thecase the method continues at step S115 else the method continues at stepS101.

At step S115 the LSP control system 12 switches to the off mode. Themethod then continues at step S101.

It is to be understood that a similar method to the method illustratedin FIG. 10 may be applied in respect of other intervention events suchas an SCS intervention event or a TCS intervention event. In the case ofan SCS intervention vent, at step S105 a determination is made whetheryawrate_err>SCS_yawrate_err_thresh_1 and at step S113 a determination ismade whether yawrate_err>SCS_yawrate_err_thresh_2.

In the case of a TCS intervention event, at step S105 a determination ismade whether pos_slip>TCS_slip_thresh_1 and at step S113 a determinationis made whether pos_slip>TCS_slip_thresh_2.

Other arrangements may also be useful.

In some embodiments, the brake controller 13 may also configured toimplement an automatic emergency braking functionality. The brakecontroller 13 may be configured to receive a signal from a radar moduleor one or more acoustic proximity sensing systems or one or more camerasystems corresponding to a distance from the vehicle 100 of an objectahead of the vehicle 100, and an angle between a longitudinal axis ofthe vehicle and a notional straight line from the vehicle to the object.If the vehicle speed is below a predetermined speed and the brakecontroller 13 determines that the object is moving into a path of thevehicle 100, the brake controller 13 may be configured to perform anautomatic emergency braking operation in which the controller 13 causesapplication of the braking system 22 to slow the vehicle 100. Thisfunctionality may be referred to as city-urban intelligent emergencybraking functionality (CUIEB) in some embodiments. The controller 13 maybe considered to trigger the performance of the automatic emergencybraking operation in some embodiments.

When the brake controller 13 triggers an automatic emergency brakingoperation, the brake controller 13 applies the braking system by causinga required amount of brake pressure to be developed in the brakingsystem 22. It is to be understood that the brake controller 13 maydetermine a required amount of brake pressure in order to perform theautomatic emergency braking operation based on a distance of the objectfrom the vehicle 100 and a speed of the vehicle 100 so as to preventcollision with the object. The controller 13 may compare the amount ofbrake pressure required for the automatic emergency braking operationwith the amount of brake pressure corresponding to any brake torquerequest signal issued by the LSP control system 12. The brake controller13 may then cause brake pressure to be developed in accordance with thatrequired to perform the automatic emergency braking operation unless theLSP control system 12 is demanding a larger amount, in which case theamount of brake pressure demanded by the LSP control system 12 may takepriority. The brake controller 13 may also terminate causing thepowertrain controller 11 to develop positive powertrain drive torque ifany positive powertrain drive torque is being requested by the LSPcontrol system 12 when the automatic emergency braking operation istriggered.

Once an automatic emergency braking operation has been triggered, if theLSP control system 12 is in the active mode the LSP control system 12may revert to the DC mode.

Some embodiments of the present invention have the advantage that abrake controller 13 will always apply the larger of the amounts of brakeforce or brake torque requested by a speed control system and a safetysystem such as a CUIEB system. Furthermore, in some embodiments thespeed control system reverts to a state in which it is unable to causethe development of positive powertrain drive torque when an emergencybraking system is triggered.

As noted above, in the case of ABS, TCS or SCS functionality, in someembodiments the speed control system is configured to revert to a lessfunctional state in the event that a value of one or more parameterstriggering an ABS, TCS or SCS intervention event exceeds a predeterminedthreshold value that is greater than the minimum threshold valuerequired to trigger the intervention event. Thus, in some embodiments anABS, TCS or SCS event will only trigger a transition to a lessfunctional state if one or more predetermined threshold values causingthe event are exceeded. Other arrangements are also useful.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, means “including but not limited to”, andis not intended to (and does not) exclude other moieties, additives,components, integers or steps.

Throughout the description and claims of this specification, thesingular encompasses the plural unless the context otherwise requires.In particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith.

1. A system comprising: a plurality of speed controllers each configuredto assume one or more ‘on’ states or one or more ‘off’ states, in apredetermined one or more on states each speed controller beingconfigured to cause a vehicle to operate in accordance with a targetset-speed value, in an off state each speed controller being configurednot to cause a vehicle to operate in accordance with a target set-speedvalue, the system being configured wherein only one of the speedcontrollers may be in an on state at a given moment in time, the otherone or more speed controllers being arranged to assume an off state whena speed controller is in an on state, the system being configured todelete from a speed controller memory or associated speed controllermemory directly accessible by each said speed controller, one or moretarget set-speed values employed by a speed controller that is not in anon state.
 2. A system according to claim 1 wherein when a speedcontroller transitions from an on state to an off state the systemdeletes from said memory one or more target set-speed values employed bythat speed controller when in an on state.
 3. A system according toclaim 1 wherein, in order to cause a vehicle to operate in accordancewith the target set-speed value, each speed controller is configured togenerate at least one of: a speed controller powertrain signal in orderto cause a powertrain to develop drive torque, and a speed controllerbrake signal in order to cause application of a brake to one or morewheels.
 4. A system according to claim 1 wherein each speed controlleris configured to cause a vehicle to operate in accordance with a targetset-speed value by causing the vehicle to operate at a speedsubstantially equal to the target set-speed value.
 5. A system accordingto claim 1 wherein each of the plurality of speed controllers isconfigured to assume one of a plurality of ‘on’ states.
 6. A systemaccording to claim 5 wherein each of the speed controllers is may assumea first or second on state, in the second on state each speed controllerbeing configured not to cause the vehicle to operate in accordance withthe target set-speed value.
 7. A system according to claim 1 wherein thevalue of one or more target set-speeds stored in said memory are deletedby overwriting the one or more stored target set-speed values.
 8. Asystem according to claim 1 configured wherein when a speed controlleris in an off condition, a value of target set-speed previously employedby that speed controller when in an on condition is retained in a memoryof the system that is not accessible to the plurality of speedcontrollers and from which none of the speed controllers can retrievethe target set-speed value when the speed controller transitions to anoff state.
 9. A system according to claim 8 configured to retain thevalue of target set-speed used by a speed controller in a secure memorybeing a memory that is not accessible to the plurality of speedcontrollers when the speed controller transitions to an off state.
 10. Asystem according to claim 8 operable to retrieve the value of targetset-speed used by a speed controller from the secure memory when saidspeed controller is not in an off state.
 11. A system according to claim10 wherein each of the plurality of speed controllers is configured toassume one of a plurality of ‘on’ states operable to retrieve the valueof target set-speed used by a speed controller from the secure memorywhen said speed controller subsequently assumes an on state.
 12. Asystem according to claim 1 configured wherein if the first speedcontroller is in an on state and a request is received to cause a secondspeed controller to assume an on state, the system is configured toallow the second speed controller to assume an on state at least in partin dependence on whether the first speed controller is causingapplication of a braking system.
 13. A system according to claim 12configured wherein if the first speed controller is in an on state and arequest is received to cause a second speed controller to assume an onstate, the system is configured not to allow the second speed controllerto assume an on state if the first speed controller is causingapplication of a braking system.
 14. A system according to claim 1wherein at least one of the speed controllers is a controller of acruise control system.
 15. A system according to claim 1 wherein atleast one of the speed controllers is a controller of an on-highwaycruise control system and at least one of the speed control systems is acontroller of an off-road cruise control system.
 16. A vehiclecomprising a system according to claim
 1. 17. A vehicle according toclaim 16 comprising a chassis, a body attached to said chassis, aplurality of wheels, a powertrain to drive said wheels, and a brakingsystem to brake said wheels.
 18. A method of controlling a motor vehiclecomprising: causing each of a plurality of speed controllers to assumeone of or more ‘on’ states and one or more ‘off’ states, when acontroller is in a predetermined one or more on states the methodcomprising causing a vehicle to operate in accordance with a targetset-speed value by means of said controller that is in an on state, whena controller is in an off state the method comprising not causing avehicle to operate in accordance with a target set-speed value by meansof said controller that is in an off state, the method comprisingallowing only one of the speed controllers to be in an on state at agiven moment in time and causing the other one or more speed controllersto assume an off state when a speed controller is in an on state, themethod further comprising not retaining in a memory accessible by eachsaid speed controller a target set-speed value employed by a speedcontroller that is not in an on state. 19-34. (canceled)
 35. Anon-transient computer readable medium loaded with a computer programthat, when executed on a processor, implements the method of claim 18.36. A processor arranged to implement the method of: causing each of aplurality of speed controllers to assume one of or more ‘on’ states andone or more ‘off’ states, when a controller is in a predetermined one ormore on states the method comprising causing a vehicle to operate inaccordance with a target set-speed value by means of said controllerthat is in an on state, when a controller is in an off state the methodcomprising not causing a vehicle to operate in accordance with a targetset-speed value by means of said controller that is in an off state, themethod comprising allowing only one of the speed controllers to be in anon state at a given moment in time and causing the other one or morespeed controllers to assume an off state when a speed controller is inan on state, the method further comprising not retaining in a memoryaccessible by each said speed controller a target set-speed valueemployed by a speed controller that is not in an on state. 37.(canceled)